High capacity lithium ion battery formation protocol and corresponding batteries

ABSTRACT

Battery formation protocols are used to perform initial charging of batteries with lithium rich high capacity positive electrode to result a more stable battery structure. The formation protocol generally comprises three steps, an initial charge step, a rest period under an open circuit and a subsequent charge step to a selected partial activation voltage. The subsequent or second charge voltage is selected to provide for a desired degree of partial activation of the positive electrode active material to achieve a desired specific capacity while providing for excellent stability with cycling. The formation protocol is particularly effective to stabilize cycling for compositions with moderate lithium enrichment.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending U.S. patentapplication Ser. No. 13/213,756 filed on Aug. 19, 2011 (publishedapplication 2012/0056590, hereinafter the '590 application) to Amiruddinet al., entitled “Very Long Cycling of Lithium Ion Batteries WithLithium Rich Cathode Materials,” incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to initial charging for formation of lithium ionbatteries with high specific capacity positive electrode activematerials. The invention further relates to batteries formed using animproved formation protocol.

BACKGROUND OF THE INVENTION

Rechargeable lithium ion batteries, also known as secondary lithium ionbatteries are desirable as power sources for a wide range ofapplications. Their desirability stems from their relative high energydensity. The capacities of secondary lithium ion batteries have beengreatly improved with the development of high capacity lithium richmetal oxides for use as positive electrode active materials. Withcycling, however, secondary lithium ion batteries generally havedecreased performance with increased cycle number. For some importantapplications, such as vehicle application, it is desired that secondarylithium ion batteries be able to charge and recharge for many cycleswithout a great loss of performance.

SUMMARY OF THE INVENTION

In a first aspect, the invention pertains to a method for the formationof a lithium ion secondary battery comprising a lithium rich metal oxidecomposition, a negative electrode, a separator between the positiveelectrode and negative electrode, and an electrolyte comprising lithiumions. The method comprises performing a first charge of the battery to avoltage from about 2.1 V to about 4.225V; after completing the firstcharge, holding the battery at an open circuit for a rest period of atleast about 6 hours; and performing a second charge after the completionof the rest period to a voltage from about 4.275V to about 4.39V. Insome embodiments, the first charge of the battery is to a voltage fromabout 2.5V to about 4.22V. In some embodiments, the battery is held atan open circuit rest period from about 8 hours to about 8 days. In someembodiments, the second charge after the rest period is to a voltagefrom about 4.28V to about 4.38V. The lithium rich metal oxide of thebattery is approximately represented by x Li₂MnO₃.(1−x)LiNi_(u)Mn_(v)Co_(w)A_(y)O₂, wherein z=0 and the stoichiometry definesx, u, v, w and y in terms of b, α, β, γ and δ, and wherein0.125≦x≦0.325. The negative electrode can comprise graphitic carbon.After charging the battery to 4.35V and storing the battery at an opencircuit voltage for one week, the negative electrode of the batterycomprises no more than about 125 ppm of the combination of Mn, Co andNi. After cycling the battery for 2500 cycles between 4.24V to 2.73V ata 1 C charge and 2 C discharge, the battery maintains at least 92% ofcapacity. The electrolyte of the battery can comprise LiPF₆ and/or LiBF₄at a total concentration from about 0.9M to about 2.5M and a solventcomprising ethylene carbonate and an organic solvent comprising dimethylcarbonate, methyl ethyl carbonate, γ-butyrolactone, γ-valerolactone or acombination thereof. In some embodiments, the electrolyte furthercomprises a lithium salt additive.

In a second aspect, the invention pertains to a lithium ion battery thatcomprises a positive electrode comprising an active material, a negativeelectrode, a separator between the positive electrode and negativeelectrode, and an electrolyte comprising lithium ions. The positiveelectrode active material comprises a lithium rich metal oxide that canbe approximately represented by the formulaLi_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2−z)F_(z), where b ranges from about0.01 to about 0.3, α ranges from 0 to about 0.4, β range from about 0.2to about 0.65, γ ranges from about 0 to about 0.46, δ ranges from about0.001 to about 0.15, and z ranges from 0 to about 0.2 with the provisothat both α and γ are not zero, and where A is a metal different fromNi, Mn and Co or a combination thereof. After charging the battery to4.35V, storing the charged battery with an open circuit for a week andfully discharging the battery, the negative electrode comprises no morethan about 150 ppm by weight manganese. In some embodiments, aftercharging the battery to 4.35V and storing the battery in an open circuitvoltage for 1 week, the negative electrode of the battery comprises nomore than about 135 ppm by weight manganese. In some embodiments, aftercharging the battery to 4.35V and storing the battery at an open circuitvoltage for a week, the negative electrode of the battery comprises nomore than about 200 ppm of the combination of Mn, Co and Ni. In someembodiments, the lithium rich metal oxide of the battery isapproximately represented by x Li₂MnO₃.(1−x)LiNi_(u)Mn_(v)Co_(w)A_(y)O₂, wherein z=0 and the stoichiometry definesx, u, v, w and y in terms of b, α, β, γ and δ, with 0.125≦x≦0.325. Insome embodiments, the lithium rich metal oxide of the positive electrodeof the battery can have a stabilization coating. The negative electrodeof the battery can comprise graphitic carbon. The electrolyte of thebattery can comprise LiPF₆ and/or LiBF₄ at a total concentration fromabout 0.9M to about 2.5M and a solvent comprising ethylene carbonate andan organic solvent comprising dimethyl carbonate, methyl ethylcarbonate, γ-butyrolactone, γ-valerolactone or a combination thereof.

The positive electrode active material of the battery can have adischarge specific capacity at a rate of 2 C from 4.35V to 2.5V at the10th discharge cycle that is at least about 140 mAh/g and that is atleast 87.5% of the discharge specific capacity at a rate of C/5 from4.35V to 2.5V at the 11th discharge cycle. When cycled at a rate of C/3from 4.35V to 2.5V the positive electrode active material of the batterycan have a discharge specific capacity at the 5th discharge cycle thatis at least about 160 mAh/g and having a calendar life at an 85% stateof charge at 30 degree C. of at least about 2 years based on dischargecapacity decay of no more than about 20%. The lithium ion battery canhave a discharge energy density of at least about 150 Wh/kg at adischarge rate of C/3 from 4.35V to 2V.

In a third aspect, the invention pertains to a lithium ion battery thatcomprises a positive electrode comprising a positive electrode materialthat comprises a lithium rich metal oxide composition; a negativeelectrode comprising a lithium intercalation/alloying composition; anon-aqueous electrolyte comprising lithium ions; and a separator betweenthe negative electrode and the positive electrode. The battery has beencycled through a formation cycle and at the 200th charge/dischargecycle, the battery has a specific discharge capacity based on the massof the lithium rich metal oxide composition of at least about 140 mAh/gat a discharge rate of 1 C from 4.35V to 2.0V that is at least about 97%of the 5th cycle specific discharge capacity. In some embodiments, thelithium rich metal oxide of the battery is approximately represented byx Li₂MnO₃.(1−x) LiNi_(u)Mn_(v)Co_(w)A_(y)O₂, wherein z=0 and thestoichiometry defines x, u, v, w and y in terms of b, α, β, γ and δ,with 0.125≦x≦0.325. In some embodiments, the lithium rich metal oxide ofthe positive electrode of the battery can have a stabilization coating.The negative electrode of the battery can comprise graphitic carbon. Theelectrolyte of the battery can comprise LiPF₆ and/or LiBF₄ at a totalconcentration from about 0.9M to about 2.5M and a solvent comprisingethylene carbonate and an organic solvent comprising dimethyl carbonate,methyl ethyl carbonate, γ-butyrolactone, γ-valerolactone or acombination thereof.

The positive electrode active material of the battery can have adischarge specific capacity at a rate of 2 C from 4.35V to 2.5V at the10th discharge cycle that is at least about 140 mAh/g and that is atleast 87.5% of the discharge specific capacity at a rate of C/5 from4.35V to 2.5V at the 11th discharge cycle. When cycled at a rate of C/3from 4.35V to 2.5V the positive electrode active material of the batterycan have a discharge specific capacity at the 5th discharge cycle thatis at least about 160 mAh/g and having a calendar life at an 85% stateof charge at 30 degree C. of at least about 2 years based on dischargecapacity decay of no more than about 20%. The lithium ion battery canhave a discharge energy density of at least about 150 Wh/kg at adischarge rate of C/3 from 4.35V to 2V.

In a fourth aspect, the invention pertains to a lithium ion battery thatcomprises a positive electrode comprising an active material, a negativeelectrode, a separator between the positive electrode and negativeelectrode, and an electrolyte comprising lithium ions. The positiveelectrode active material comprises a lithium rich metal oxide that canbe approximately represented by the formulaLi_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2−z)F_(z), where b ranges from about0.01 to about 0.3, α ranges from 0 to about 0.4, β range from about 0.2to about 0.65, γ ranges from about 0 to about 0.46, δ ranges from about0.001 to about 0.15, and z ranges from 0 to about 0.2 with the provisothat both α and γ are not zero, and where A is a metal different fromNi, Mn and Co or a combination thereof. The positive electrode has adischarge specific capacity at a rate of 2 C from 4.35V to 2.5V at the10th discharge cycle that is at least about 140 mAh/g and that is atleast 87.5% of the discharge specific capacity at a rate of C/5 from4.35V to 2.5V at the 11th discharge cycle. The positive electrode activematerial of the battery can have a discharge specific capacity at a rateof 2 C from 4.35V to 2.5V at the 10th discharge cycle that is at least89% to about 92.5% of the discharge specific capacity at a rate of C/5from 4.35V to 2.5V at the 11th discharge cycle. In some embodiments, thelithium rich metal oxide of the battery can be approximately representedby x Li₂MnO₃.(1−x) LiNi_(u)Mn_(v)Co_(w)A_(y)O₂, wherein z=0 and thestoichiometry defines x, u, v, w and y in terms of b, α, β, γ and δ, and0.125≦x≦0.325. The negative electrode of the battery can comprisegraphitic carbon.

In a fifth aspect, the invention pertains to a lithium ion battery thatcomprises a positive electrode comprising an active material, a negativeelectrode, a separator between the positive electrode and negativeelectrode, and an electrolyte comprising lithium ions. The positiveelectrode active material comprises a lithium rich metal oxide that canbe approximately represented by the formulaLi_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2−z)F_(z), where b ranges from about0.01 to about 0.3, α ranges from 0 to about 0.4, β range from about 0.2to about 0.65, γ ranges from about 0 to about 0.46, δ ranges from about0.001 to about 0.15, and z ranges from 0 to about 0.2 with the provisothat both α and γ are not zero, and where A is a metal different fromNi, Mn and Co or a combination thereof. The positive electrode activematerial of the battery can have a discharge specific capacity at a rateof C/3 from 4.35V to 2.5V at the 5th discharge cycle that is at leastabout 160 mAh/g and having a calendar life at an 85% state of charge at30 degrees C. of at least about 2 years based on discharge capacitydecay of no more than about 20%. In some embodiments, the positiveelectrode active material of the battery can have a calendar life at 30degree C. of at least about 3 years based on discharge capacity decay ofno more than about 20%. In some embodiments, the lithium rich metaloxide of the battery can be approximately represented by x Li₂MnO₃.(1−x)LiNi_(u)Mn_(v)Co_(w)A_(y)O₂, wherein z=0 and the stoichiometry definesx, u, v, w and y in terms of b, α, β, γ and δ, and wherein0.125≦x≦0.325. The negative electrode of the battery can comprisegraphitic carbon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a pouch cell battery showing the innerelectrode plates.

FIG. 2 is a plot of discharge capacities versus cycle numbers ofbatteries 1 a and 1 b at different discharge rates.

FIG. 3 is a plot of differential capacity versus voltage of batteries 1f with graphitic carbon electrode activated under different formationconditions with enlarged portions 3A and 3B showing changes of manganeseactivity.

FIG. 4 is a plot of differential capacity versus voltage of batteries 1g-1 j with lithium metal electrode activated under different formationconditions with enlarged portion 4A showing activation of Li₂MnO₃.

FIG. 5 is a plot of resistance versus percentage of state of charge (SOC%) of batteries 1 k, 1 l, and 1 m formed under formation protocols 1, 2,and 3 respectively.

FIG. 6 is a plot of power versus SOC % of batteries 1 n and 1 o that hasa design capacity of roughly 27 Ah.

FIG. 7 is a plot of normalized discharge capacity and average voltageversus cycle number of batteries 1 p and 1 q cycled out to 2500 cycles.

FIG. 8 is a plot of percentage of permanent capacity loss versus monthsof storage at 30 degree C. for battery 1 r formed with formationprotocol 1, battery is formed with formation protocol 3, and a controlbattery.

FIG. 9 is a plot of percentage of permanent capacity loss versus monthsof storage at 45 degree C. for battery 1 t formed with formationprotocol 1, battery 1 u formed with formation protocol 3, and a controlbattery.

FIG. 10 is a plot of capacity versus cycle number of batteries 1 v and 1w activated with formation protocols 1 and 2 respectively at roomtemperature.

FIG. 11 is a plot of capacity versus cycle number of batteries 1 x and 1y activated with formation protocols 1 and 2 respectively at 45 degreeC.

FIG. 12 is a plot of capacity versus cycle number of batteries a, b, c,d, e activated with formation protocol 2 and different second agingperiods.

FIG. 13 is a plot of voltage versus capacity of batteries f and g formedwith a graphitic carbon electrode and a lithium counter electrode withand without lithium salt additive respectively.

FIG. 14 is a plot of voltages of a three electrode battery during thecourse of a two step formation protocol.

DETAILED DESCRIPTION OF THE INVENTION

An improved approach is described for the activation or formation of alithium ion battery comprising a high capacity positive electrode activematerial. During the first charge of a lithium ion battery, significantirreversible chemical changes take place within the battery, and thefirst charge of the battery can be referred to as a formation process inwhich the battery condition changes to a form for cycling. Thus, toachieve a stable formed battery, the first charge of the battery can beperformed according to a specific process called a formation protocol,which can be designed to contribute to more stable cycling of thebattery. The formation protocol herein is designed to take advantage ofchemical changes taking place within the battery. For example, a solidelectrolyte interface (SEI) layer forms around the anode activematerial, and the stability of the SEI layer is believed to besignificant for stable cycling of the battery. With lithium rich highcapacity positive electrode active materials, it has been found thatsignificant structural changes also take place with respect to thepositive electrode active materials also. Specifically, for the lithiumrich positive electrode active materials described, the irreversiblechanges to the battery during the first charge can comprise activationof the material to make some phases of the material available forsubsequent cycling. An improved formation protocol is described that isfound to significantly stabilize the batteries during cycling as well asduring storage. In particular, the formation protocol comprises aninitial charge to a voltage from about 4.125 V to about 4.225V, a restperiod at an open circuit voltage and then a charge to a voltage fromabout 4.275V to about 4.4V.

In some circumstances, deterioration of the positive electrode activematerial during activation is found to result in decomposition of thematerial that results in dissolution of transition metals from thematerial into the electrolyte and ultimate migration of the transitionmetal atoms to the negative electrode. It can be expected that thedecomposition of the positive electrode active material may result inlost capacity during cycling as well as possibly less stability duringcycling. The measurement of the transition metal content in the negativeelectrode can be used as one measure of the stability of the positiveelectrode active material along with measurements of the rate of fade ofcapacity with cycling and/or changes in average voltage. Thus, improvedbattery performance can result from the improved battery formationprotocol. Shelf life is also a significant commercial parameter for abattery, and the improved formation protocol can significantly improvethe shelf life of a battery.

The difference between the first charge capacity and the first dischargecapacity can be referred to as the irreversible capacity loss, and theirreversible capacity loss is a reflection of at least some of the firstcycle irreversible changes in the battery. Generally the irreversiblecapacity loss is significantly greater than per cycle capacity loss atsubsequent cycles. The irreversible capacity loss results in acorresponding decrease in the capacity, energy and power for the cell.With respect to the negative electrode during the first charge of thebattery, a reaction involving the electrolyte results in the formationof a solvent electrolyte interphase layer associated with the negativeelectrode active material, and the presence of a stable SEI layer isbelieved to stabilize the battery with respect to electrolytedegradation during cycling. For lithium rich positive electrode activematerials described herein, significant irreversible changes also takeplace with respect to the composition of the positive electrode activematerials, and control of the irreversible changes to the positiveelectrode active materials can be used effectively to achieve verystable long term cycling properties. The formation protocol furtherprovides control of the activation of the positive electrode activematerials.

The batteries described herein are lithium-based batteries in which anon-aqueous electrolyte solution comprises lithium ions. For secondarylithium ion batteries during charge, oxidation takes place in thecathode (positive electrode) where lithium ions are extracted andelectrons are released. During discharge, reduction takes place in thecathode where lithium ions are inserted and electrons are consumed.Generally, the batteries are formed with lithium ions in the positiveelectrode material such that an initial charge of the battery transfersa significant fraction of the lithium from the positive electrodematerial to the negative electrode (anode) material to prepare thebattery for discharge. Unless indicated otherwise, performance valuesreferenced herein are at room temperature.

When the corresponding batteries with intercalation-based positiveelectrode active materials are in use, the intercalation and release oflithium ions from the lattice induces changes in the crystalline latticeof the electroactive materials. As long as these changes are essentiallyreversible, the capacity of the material does not change significantlywith cycling. However, the capacity of the active materials is observedto decrease with cycling to varying degrees. Thus, after a number ofcycles, the performance of the battery falls below acceptable values,and the battery is replaced.

The word “element” is used herein in its conventional way as referringto a member of the periodic table in which the element has theappropriate oxidation state if the element is in a composition and inwhich the element is in its elemental form, M⁰, only when stated to bein an elemental form. Therefore, a metal element generally is only in ametallic state in its elemental form or a corresponding alloy of themetal's elemental form. In other words, a metal oxide or other metalcomposition, other than metal alloys, generally is not metallic.

The lithium ion batteries can use a positive electrode active materialthat is lithium rich relative to a reference homogenous electroactivelithium metal oxide composition. The class of lithium rich positiveelectrode active materials of interest can be approximately representedwith a formula:

Li_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2−z)F_(z),  (1)

where b ranges from about 0.01 to about 0.3, α ranges from 0 to about0.4, β range from about 0.2 to about 0.65, γ ranges from about 0 toabout 0.46, δ ranges from about 0.001 to about 0.15, and z ranges from 0to about 0.2 with the proviso that both α and γ are not zero, and whereA is a metal different from Ni, Mn and Co or a combination thereof.Element A and F (fluorine) are optional cation and anion dopants,respectively. Elements A can be, for example, Mg, Sr, Ba, Cd, Zn, Al,Ga, B, Zr, Ti, Ca, Ce, Y, Nb, Cr, Fe, V, or combinations thereof. Theuse of a fluorine dopant in lithium rich metal oxides to achieveimproved performance is described in published U.S. patent application2010/0086854 to Kumar et al., entitled “Fluorine Doped Lithium RichMetal Oxide Positive Electrode Battery Materials With High SpecificCapacity and Corresponding Batteries,” incorporated herein by reference.

In some embodiments, it is believed that appropriately formedlithium-rich lithium metal oxides have a composite crystal structure.For example, in some embodiments of lithium rich materials, a layeredLi₂MO₃ material may be structurally integrated with either a layeredLiM′O₂ component, in which a reference structure has M and M′ beingmanganese, although particular compositions of interest have a portionof the manganese cations substituted with other transition metal cationswith appropriate oxidation states. In some embodiments, the positiveelectrode material can be represented in two component notation as xLi₂MO₃.(1−x)LiM′O₂ where M′ is one or more metal cations with an averagevalence of +3 with at least one cation being a manganese cation or anickel cation, and where M is one or more metal cations with an averagevalence of +4. Generally, for compositions of particular interest, M canbe considered to be Mn. The general class of compositions are describedfurther, for example, in published U.S. patent application 2011/0052981Ato Lopez et al. (the '981 application), entitled “Layer-Layer LithiumRich Complex Metal Oxides With High Specific Capacity and ExcellentCycling,” incorporated herein by reference.

The compositions expressed in the single component notation and twocomponent notation can be related. Specifically, if b+α+β+γ+δ in formula(1) above is approximately equal to 1, the material can be alayered-layered material approximately represented by the formulax.Li₂MnO₃.(1−x)LiNi_(u)Mn_(v)Co_(w)A_(y)O₂, assuming for simplicity thatz=0. With respect to the charging of a battery with the compositematerials, the lithium manganese oxide (Li₂MnO₃) component of thecompositions can undergo a reaction to release molecular oxygen with anassociated release of 2 Li ions as indicated in equation (2):

Li₂MnO₃→(MnO₂)+2Li⁺+2e ⁻+½O₂.  (2)

Upon discharge, the (MnO₂) composition takes up a single lithium ion anda single electron to form LiMnO₂ so that there is an overall significantdecrease in capacity due to the irreversible reaction of the materialduring the initial charge. The product composition is written as (MnO₂)because it is not completely clear what this material is. While Eq. (2)is balanced if (MnO₂) is actually MnO₂, it is not clear if this is theprecise reaction, although oxygen release is observed corresponding to areduction of the metal. As discussed below, evidence suggests that thereaction schematically represented in Eq. (2) takes place efficiently atvoltages above roughly 4.4 volts. Thus, with the lithium richlayered-layered material, during the first cycle charge above roughly4.2V, decomposition of a Li₂MnO₃ component in the high capacity materialcan lead to oxygen loss and a significant irreversible capacity lossattributable to the positive electrode active material. The materials inprinciple can undergo other irreversible changes that may coincide withthe initial charge step, such as a decomposition reactionLi₂MnO₃→MnO₂+Li₂O. Such a decomposition reaction does not result in ameasured irreversible capacity loss since no electrons are generatedthat would be measured during the initial charge, but such a reaction toform inert lithium oxide could result in a loss of reversible capacityrelative to the theoretical capacity for a particular weight ofmaterial. The initial reactions involving the active material are notcompletely understood. For example, evidence presented below indicatesthat only low levels of manganese dissolves into the electrolyte andmigrates to the negative electrode if the battery is stabilized throughthe use of the multiple step partial activation formation protocol.Differential capacity results are consistent with the stabilization ofthe positive electrode found with the cycling data.

The formulas presented herein for complex lithium metal oxides are basedon the molar quantities of starting materials in the synthesis, whichcan be accurately determined. With respect to the multiple metalcations, these are generally believed to be quantitatively incorporatedinto the final material with no known significant pathway resulting inthe loss of the metals from the product compositions. Of course, many ofthe metals have multiple oxidation states, which are related to theiractivity with respect to the batteries. Due to the presence of themultiple oxidation states and multiple metals, the precise stoichiometrywith respect to oxygen generally is only roughly estimated based on thecrystal structure, electrochemical performance and proportions ofreactant metals, as is conventional in the art. However, based on thecrystal structure, the overall stoichiometry with respect to the oxygenis reasonably estimated. All of the protocols discussed in thisparagraph and related issues herein are routine in the art and are thelong established approaches with respect to these issues in the field.

A two step formation protocol was previously found to stabilizebatteries with lithium rich high capacity positive electrode activematerials as described in published U.S. patent application 2011/0236751to Amiruddin et al. (the '751 application), entitled “High VoltageBattery Formation Protocols and Control of Charging and Discharging forDesirable Long Term Cycling Performance,” incorporated herein byreference. The teachings in the '751 application are based on theconcept that high voltage activation is involved to provide for theobserved high specific capacity of the active material. In contrast, thepresent formation protocol is designed to provide partial activation ofthe positive electrode active material for dramatically improved cyclingwith a reasonable portion of the specific capacity available forcycling. The outstanding cycling performance provides for both extremelystable capacity and average voltage out to over 1000 cycles withrelatively high discharge rates. Thus, the batteries are suitable forhigher power applications, such as certain vehicle applications.Evidence suggests that the partial activation formation protocoldescribed herein stabilizes the positive electrode in addition to thenegative electrode, and generally a short rest period within themultistep protocol can be used to obtain outstanding cycling stability.

The complex lithium rich metal oxides have been found to activate athigher voltages through the removal of lithium from a Li₂MnO₃-typephase. The behavior of the material with lithium extraction can beinterrogated through differential capacity plots, which can identifychanges in lithium extraction as a function of voltage. While theremoval of lithium from the Li₂MnO₃ phase can be important to achievehigh values of specific capacities of the material, the resultingphase(s) have been found to transform to unstable phases followingactivation. Thus, the high capacity lithium rich metal oxides canexhibit a capacity that decays faster than desired with cycling due todecomposition of the active material.

While some aspects of the material remain a mystery, tremendous progresshas been achieved in understanding some of the extraordinarily complexchemistry and material science of the lithium rich layered-layeredlithium metal oxides, as described in published U.S. patent application2012/0056590 to Amiruddin et al. (the '590 application), entitled “VeryLong Cycling of Lithium Ion Batteries With Lithium Rich CathodeMaterials,” incorporated herein by reference. Based on this furtherchemical understanding, fully activated material can be reasonablystabilized for long term cycling by operating the battery subsequent toactivation in an appropriate voltage window. However, additionaladvantages are achieved through partial activation of the activematerial, and the advantages of partial activation are particularlypronounced for material with lower amounts of lithium enrichment.

The formation protocol described herein provides for the desirable andstable partial activation of the batteries. Specifically, the activationprotocol described herein provides a balance with sufficient activationof the higher voltage Li₂MnO₃-type phases while not destabilizing thematerial. It has been discovered that the formation protocol can provideappropriate balancing of sufficient activation of the high voltagematerial to achieve desired initial capacities while leaving asufficiently stable material with respect to cycling. For at least somevehicle applications, it is generally desirable to have no more thanabout 20% loss of power based on capacity and average voltage for morethan 1000 charge/discharge cycles at relatively high rates. Anappropriate balance can be found with relatively high dischargecapacities and long cycling stabilities with respect to both capacityand average voltage.

While the maximum voltage during a first cycle formation charge does notneed to be the same as the charge voltage during cycling, it has beenfound that a moderate formation voltage can sufficiently activate thematerial to achieve desired capacity, and that cycling over anappropriate voltage window with a charge voltage that does notsignificantly additionally activate the active material can be effectiveto achieve stable long term cycling. In other words, with sufficientactivation to form the material at a desired capacity, the cyclingvoltage window can be selected to maintain the capacity for a very largenumber of cycles. The results are consistent with maintaining asignificant fraction of an inactive Li₂MnO₃ phase within the materialduring cycling and that the Li₂MnO₃ phase in some way stabilizes thematerial to reduce unwanted phase transitions as the material is cycledthrough charging and discharging of the battery. Material instabilitiescan result from phase transitions of the activated materials as a resultof cycling, as demonstrated in the '590 application.

The complex lithium rich metal oxide material is believed to initiallyhave a layered-layered mixed phase material domains within individualparticles with different stoichiometries. Activation induces partialphase changes, and cycling induces additional phase changes.Electrochemical measurements provide explicit evidence of multipleproduct phases that have not been clearly identified although thegeneral nature of some of the phases can be reasonably guessed. Theidentification of the phases is extraordinarily difficult due to theextreme complexity of the materials along with the dynamic nature of thechanges with cycling, the similarities of the x-ray diffractograms forsignificantly different phases and the multiphasic behavior generatingsmall domains and overlapping domains that may not generate cleardiffractions among other reasons. Thus, in many respects, theelectrochemical data is a good tool presently for identifying thepresence of various phases. Differential capacity plots in the '590application in particular provide direct evidence of the properties ofvarious phases and the phase evolution with cycling.

The formation protocol provides an initial charge step to a voltage ofno more than about 4.2V. Due to the relatively low voltage during theinitial charge, the differential capacity plots suggest that littleactivation takes place of the higher voltage phases of the positiveelectrode active material. After the first charge, the battery is storedin an open circuit configuration for a rest period. While not wanting tobe limited by theory, it is believed that the SEI layer substantiallyforms by the end of the rest period. Partial activation of the positiveelectrode active material takes place during a subsequent charge stepafter the rest period. Additional activation of the high voltage phasesof the material may or may not take place during cycling of the battery,and the degree of further activation during cycling may depend on theamount of lithium enrichment of the initial cathode material.

A rest period or second aging has been found to be important withrespect to stable formation of the battery for subsequent cycling.Specifically, after an initial low voltage charge, the battery can bestored in an open circuit rest period which generally extends for atleast six hours. With the partial activation described herein, arelatively shorter rest period can be effectively used to stabilize thebattery for higher capacity cycling in comparison to the formationprotocol with full activation described in the '751 application. Therole of the rest period is not well understood, but experimental resultsindirectly suggest a thickening of the SEI layer. In any case, theperformance results clearly show significance associated with the restperiod. Also, a rest period that is too long also deteriorates thecycling performance significantly.

The second charge step after the rest period is selected to partiallyactivate the positive electrode active material and to clearly avoidexcessive activation. Thus, the second charge step is selected to have avoltage that is in the range from about 4.275V to about 4.39V. Theselection of the full charge voltage allows for sufficient activation ofthe desired degree of capacity of the positive electrode active materialwhile maintaining the desired stability of the material.

The positive electrode active material is stabilized by the improvedformation protocol relative to a formation protocol involving a singlecharge during formation. The increased stability is suggested by thegeneration of a reduced amount of gaseous oxygen during the formationprocess. Gaseous oxygen can be associated with irreversible changes tothe positive electrode active material. The production of gaseous oxygenis undesirable also from a production perspective since oxygen should bevented from a battery to avoid mechanical instability of the battery.The venting of the oxygen can be an undesirable production complicationduring the formation charge process if a significant amount of oxygen isreleased.

The stability of the positive electrode active material is furtherevidenced by the analysis of the battery after activation, which isconsistent with the reduced release of oxygen during formation. It hasbeen found that if the cathode material is unstable, manganese and to alesser extent other transition metals dissolve into the electrolyte fromthe positive electrode, which results in eventual deposition in thenegative electrode active material. Using the improved formationprotocol described herein, the batteries can be activated with very lowlevels of transition metals found in the negative electrode activematerial. Specifically, after activation and storage of chargedbatteries as described further below, the negative electrode cancomprise no more than about 150 ppm by weight manganese and no more thanabout 200 ppm by weight total transition metals not native to thenegative electrode active material. The low dissolution of transitionmetals is consistent with the stability of the capacity with cyclingover a large number of cycles. We note that while generally the resultsin the '590 application did not involve a two step formation protocol,the long term cycling results in the '590 application were obtained withthe two step partial activation formation protocol described herein.

In addition to stabilizing the electrodes, the improved formationprotocol also surprisingly improves the rate capability of the material.Thus, even at low cycle numbers, the batteries formed with the improvedformation protocol exhibit surprisingly improved high rate specificcapacities relative to fully activated batteries. The specificcapacities generally decrease with discharge rate. The effect ofdischarge rate can be examined by the percent decrease in specificcapacity as the rate increases. Since greater activation of the batteryis believed to initially increase the capacity at the expenses ofdecreased cycling stability, it is surprising that the relative capacityincrease from full activation can effectively decrease or essentiallydisappear for rate of 1 C, 2 C or higher relative to the partiallyactivated batteries. In conventional notation, a rate of 1 C correspondswith the discharge of the battery over a one hour time period, while arate of 2 C corresponds with discharge over ½ hour and C/3 correspondswith discharge of the battery over three hours. Thus, at high dischargerates, the batteries activated with the multiple step partial activationformation protocol exhibit surprisingly large specific capacities.

Also, the batteries formed with positive electrodes activated with themultiple step partial activation protocol described herein also exhibita reduced DC resistance. The DC resistance is a measure of the internalelectrical resistance within the battery, and a measurement procedurefor the DC resistance is described in detail below. If the DC resistanceof the battery is greater, more heat is generated by the battery duringdischarge and less energy is available from the battery for externalwork. In general, the values of the DC resistance are more significantat battery states of charge that are of most significance during actualuse of the battery. Thus, for convenience, the DC resistance is examinedbelow at a battery state of charge from 20% to 90%. Generally, themultiple step partial activation formation protocol can reduce the DCresistance over the state of charge from 20% to 90% by at least about 5%relative to batteries formed with full activation.

Using the partial activation formation protocol, it is also found thatshelf life of the batteries is also significantly improved. Forpractical commercial batteries, the batteries should exhibit areasonable shelf life. Upon storage of a battery prior to use, thebattery can exhibit permanent loss of capacity. The permanent loss ofcapacity can be desired to be below a specific percent prior todetermining that the battery is wasted. Since the formation step isperformed under certain desirable conditions, lithium ion batteries aregenerally distributed following a formation cycle and possibly a fewcycles of the battery. When properly formed, the batteries can then bestored at 30° C. for at least 24 months with degradation of the batterycapacity of no more than about 10% permanent capacity loss. In general,a calendar life is desired with at least 70% capacity retention afterstorage for, for example, 5 years or 10 years at room temperature. Fortesting purposes, the batteries are stored after discharging a batteryto an 80% state of charge, and similar storage can be performed forcommercial batteries. The stored batteries are removed periodically andcycled to evaluate the permanent capacity loss. After a year of datacollection at, for example, monthly increments, the incrementalmeasurements can be extrapolated for the 5 years to 10 years to predictthe calendar life.

The batteries in the examples involve graphitic carbon active materialsin the negative electrodes. However, the improved performance of thepositive electrode active materials through the manipulation andappropriate stabilization of the materials can be extended to othernegative electrode active materials that intercalate or alloy withlithium. The electrodes can be assembled into appropriate batteryformats.

In summary, the improved formation protocol with partial activation ofthe positive electrode active material can provide extremely stablecycling out to a large number of cycles, improved rate performance anddesirable shelf life. The stabilized batteries formed with theparticular formation protocol exhibit significant decreases indissolution of manganese and other transition metals from the cathode asdemonstrated through an examination of metal uptake into the anode.Thus, the improved formation protocol can be effectively used for theinitial preparation of commercial batteries, including vehiclebatteries, that are expected to have desirable performance out to alarge number of charge/discharge cycles.

Lithium Ion Batteries

Lithium ion batteries generally comprise a positive electrode, anegative electrode, a separator between the negative electrode and thepositive electrode and an electrolyte comprising lithium ions. Theelectrodes are generally associated with metal current collectors.Lithium ion batteries refer to batteries in which the negative electrodeactive material is a material that takes up lithium during charging andreleases lithium during discharging. A battery can comprise multiplepositive electrodes and multiple negative electrodes, such as in astack, with appropriately placed separators. Electrolyte in contact withthe electrodes provides ionic conductivity through the separator betweenelectrodes of opposite polarity. A battery generally comprises currentcollectors associated respectively with negative electrode and positiveelectrode. The basic battery structures and compositions are describedin this section.

The nature of the negative electrode intercalation/alloying materialinfluences the resulting voltage of the battery since the voltage is thedifference between the half cell potentials at the cathode and anode.Suitable negative electrode (anode) lithium intercalation/alloyingcompositions can include, for example, graphite, synthetic graphite,coke, fullerenes, other graphitic carbons, niobium pentoxide, tinalloys, silicon, titanium oxide, tin oxide, and lithium titanium oxide,such as Li_(x)TiO₂, 0.5<x≦1 or Li_(1+x)Ti_(2−x)O₄, 0≦x≦⅓. The graphiticcarbon and metal oxide negative electrode compositions take up andrelease lithium through an intercalation or similar process. Silicon andtin alloys form alloys with the lithium metal to take up lithium andrelease lithium from the alloy to correspondingly release lithium.Additional negative electrode materials are described in published U.S.patent applications 2010/0119942 to Kumar, entitled “CompositeCompositions, Negative Electrodes with Composite Compositions andCorresponding Batteries,” and 2009/0305131 to Kumar et al., entitled“High Energy Lithium Ion Batteries with Particular Negative ElectrodeCompositions,” both of which are incorporated herein by reference.Desirable elemental silicon based negative electrode active materialsare described in published U.S. patent application number 2011/0111294filed on Nov. 3, 2010 to Lopez et al., entitled “High Capacity AnodeMaterials for Lithium Ion Batteries,” incorporated herein by reference.Desirable silicon oxide based negative electrode active materials aredescribed in copending U.S. patent application Ser. No. 13/108,708 filedon May 16, 2011 to Deng et al., entitled “Silicon Oxide Based HighCapacity Anode Materials for Lithium Ion Batteries,” incorporated hereinby reference.

The positive electrode active compositions and negative electrode activecompositions generally are powder compositions that are held together inthe corresponding electrode with a polymer binder. The binder providesionic conductivity to the active particles when in contact with theelectrolyte. Suitable polymer binders include, for example,polyvinylidine fluoride, polyethylene oxide, polyethylene,polypropylene, polytetrafluoroethylene, polyacrylates, rubbers, e.g.ethylene-propylene-diene monomer (EPDM) rubber or styrene butadienerubber (SBR), copolymers thereof, or mixtures thereof. The particleloading in the binder can be large, such as greater than about 80 weightpercent. To form the electrode, the powders can be blended with thepolymer in a suitable liquid, such as a solvent for the polymer. Theresulting paste can be pressed into the electrode structure.

The positive electrode composition, and possibly the negative electrodecomposition, generally also comprises an electrically conductive powderdistinct from the electroactive composition. Suitable supplementalelectrically conductive powders include, for example, graphite, carbonblack, metal powders, such as silver powders, metal fibers, such asstainless steel fibers, and the like, and combinations thereof.Generally, a positive electrode can comprise from about 1 weight percentto about 25 weight percent, and in further embodiments from about 2weight percent to about 15 weight percent distinct electricallyconductive powder. A person of ordinary skill in the art will recognizethat additional ranges of amounts of electrically conductive powders andpolymer binders within the explicit ranges above are contemplated andare within the present disclosure.

The electrode generally is associated with an electrically conductivecurrent collector to facilitate the flow of electrons between theelectrode and an exterior circuit. The current collector can comprisemetal, such as a metal foil or a metal grid. In some embodiments, thecurrent collector can be formed from nickel, aluminum, stainless steel,copper or the like. The electrode material can be cast as a thin filmonto the current collector. The electrode material with the currentcollector can then be dried, for example in an oven, to remove solventfrom the electrode. In some embodiments, the dried electrode material incontact with the current collector foil or other structure can besubjected to a pressure, such as, from about 2 to about 10 kg/cm²(kilograms per square centimeter).

The separator is located between the positive electrode and the negativeelectrode. The separator is electrically insulating while providing forat least selected ion conduction between the two electrodes. A varietyof materials can be used as separators. Commercial separator materialsare generally formed from polymers, such as polyethylene and/orpolypropylene that are porous sheets that provide for ionic conduction.Commercial polymer separators include, for example, the Celgard® line ofseparator material from Hoechst Celanese, Charlotte, N.C. Also,ceramic-polymer composite materials have been developed for separatorapplications. These composite separators can be stable at highertemperatures, and the composite materials can significantly reduce thefire risk. The polymer-ceramic composites for separator materials aredescribed further in U.S. patent application 2005/0031942A to Hennige etal., entitled “Electric Separator, Method for Producing the Same and theUse Thereof,” incorporated herein by reference. Polymer-ceramiccomposites for lithium ion battery separators are sold under thetrademark Separion® by Evonik Industries, Germany.

We refer to solutions comprising solvated ions as electrolytes, andionic compositions that dissolve to form solvated ions in appropriateliquids are referred to as electrolyte salts. Electrolytes for lithiumion batteries can comprise one or more selected lithium salts.Appropriate lithium salts generally have inert anions. Suitable lithiumsalts include, for example, lithium hexafluorophosphate, lithiumhexafluoroarsenate, lithium bis(trifluoromethyl sulfonyl imide), lithiumtrifluoromethane sulfonate, lithium tris(trifluoromethyl sulfonyl)methide, lithium tetrafluoroborate, lithium perchlorate, lithiumtetrachloroaluminate, lithium chloride, lithium difluoro oxalato borate,lithium bis-oxalato borate, and combinations thereof. Traditionally, theelectrolyte comprises a 1 M concentration of the lithium salts, althoughgreater or lesser concentrations can be used.

For lithium ion batteries of interest, a non-aqueous liquid is generallyused to dissolve the lithium salt(s). The solvent generally does notdissolve the electroactive materials. Appropriate solvents include, forexample, propylene carbonate, dimethyl carbonate, diethyl carbonate,2-methyl tetrahydrofuran, dioxolane, tetrahydrofuran, methyl ethylcarbonate, γ-butyrolactone, dimethyl sulfoxide, acetonitrile, formamide,dimethyl formamide, triglyme (tri(ethylene glycol) dimethyl ether),diglyme (diethylene glycol dimethyl ether), DME (glyme or1,2-dimethyloxyethane or ethylene glycol dimethyl ether), nitromethaneand mixtures thereof.

Particularly useful electrolytes for high voltage lithium-ion batteriesare described further in published U.S. patent application 2011/0136019filed on Dec. 4, 2009 to Amiruddin et al. (the '019 application),entitled “Lithium Ion Battery With High Voltage Electrolytes andAdditives,” incorporated herein by reference. The high voltageelectrolytes can comprise LiPF₆ and/or LiBF₄ at a total concentrationfrom about 0.9M to about 2.5M and a solvent comprising ethylenecarbonate and a liquid organic solvent comprising dimethyl carbonate,methyl ethyl carbonate, γ-butyrolactone, γ-valerolactone or acombination thereof. To stabilize the cycling properties of batterieswith the electrolytes, the electrolytes can further comprise from about0.01 weight percent to about 5 weight percent of a lithium saltadditive, such as lithium difluoro oxalato borate or lithiumbis(oxalato)borate or an organic additive, such as vinylene carbonate.Also, high voltage electrolytes with good low temperature behavior aredescribed in copending U.S. patent application Ser. No. 13/325,367 to Liet al., entitled “Low Temperature Electrolyte for High Capacity LithiumBased Batteries,” incorporated herein by reference.

The electrodes described herein can be incorporated into variouscommercial battery designs. For example, the cathode compositions can beused for prismatic shaped batteries, wound cylindrical batteries, coinbatteries or other reasonable battery shapes. The batteries can comprisea single cathode structure or a plurality of cathode structuresassembled in parallel and/or series electrical connection(s).

In some embodiments, the positive electrode and negative electrode canbe stacked with the separator between them, and the resulting stackedstructure can be placed into a cylindrical or prismatic configuration toform the battery structure. Appropriate electrically conductive tabs canbe welded or the like to the current collectors, and the resultingjellyroll or stack structure can be placed into a metal canister orpolymer package, with the negative tab and positive tab welded toappropriate external contacts. Electrolyte is added to the canister, andthe canister is sealed to complete the battery. Some presently usedrechargeable commercial batteries include, for example, the cylindrical18650 batteries (18 min in diameter and 65 mm long) and 26700 batteries(26 mm in diameter and 70 mm long), although other battery sizes can beused.

A schematic diagram of a pouch battery is shown in FIG. 1. Specifically,a pouch cell battery 120 is shown schematically having a negativeelectrode 122, a positive electrode 124 and a separator 126 betweennegative electrode 122 and positive electrode 124. A pouch battery cancomprise multiple positive electrodes and multiple negative electrodes,such as in a stack, with appropriately placed separators. Electrolyte incontact with the electrodes provides ionic conductivity through theseparator between electrodes of opposite polarity. A battery generallycomprises current collectors 128, 130 associated respectively withnegative electrode 122 and positive electrode 124. The stack ofelectrodes and separators can be enclosed in a laminated film casing132. With respect to some specific embodiments, pouch batteries can beconstructed as described in U.S. Pat. No. 8,187,752 to Buckley et al,entitled “High Energy Lithium Ion Secondary Batteries”, and publishedU.S. patent application 2012/0028105 to Kumar et al., entitled, “BatteryPacks for Vehicles and High Capacity Pouch Secondary Batteries forIncorporation Into Compact Battery Packs,” both of which areincorporated herein by reference.

Cathode Active Material

The positive electrode active materials of particular interest compriselithium rich compositions that generally are believed to form alayered-layered composite crystal structure. In some embodiments, thelithium metal oxide compositions specifically comprise Ni, Co and Mnions with an optional metal dopant. A lithium rich composition can bereferenced relative to a composition LiMO₂, where M is one or moremetals with an average oxidation state of +3. Generally, the lithiumrich compositions can be represented approximately with a formulaLi_(1+x)M_(1−y)O₂, where M represents one or more non-lithium metals,x≧0, and y is related to x based on the average valence of the metals.When x is greater than 0, the composition is lithium rich relative tothe reference LiMO₂ composition. In some embodiments, x is from about0.01 to about 0.33, and y is from about x−0.2 to about x+0.2 with theproviso that y≧0. In the layered-layered composite compositions, x isapproximately equal to y. In general, the additional lithium in thelithium rich compositions is accessed at higher voltages such that theinitial charge takes place at a relatively higher voltage to access theadditional capacity. However, as described herein the material canundergo irreversible changes during an initial high voltage charge step,such that the material that cycles subsequent to the initial charge isnot the same material that reacts at high voltage in the initialmaterial.

Lithium rich positive electrode active materials of particular interestcan be represented approximately by a formulaLi_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2−z)F_(z), where b ranges from about0.01 to about 0.3, α ranges from about 0 to about 0.4, β range fromabout 0.2 to about 0.65, γ ranges from 0 to about 0.46, δ ranges from 0to about 0.15 and z ranges from 0 to about 0.2 with the proviso thatboth α and γ are not zero, and where A is a metal different from Mn, Ni,or Co, such as Mg, Sr, Ba, Cd, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb, Cr,Fe, V, Li or combinations thereof. A person of ordinary skill in the artwill recognize that additional ranges of parameter values within theexplicit compositional ranges above are contemplated and are within thepresent disclosure. To simplify the following discussion in thissection, the optional fluorine dopant is not discussed further, althoughthe option of a fluorine dopant should still be considered for theparticular embodiments. Desirable lithium rich compositions with afluorine dopant are described further in published U.S. patentapplication 2010/0086854A to Kumar et al., entitled “Fluorine DopedLithium Rich Metal Oxide Positive Electrode Battery Materials With HighSpecific Capacity and Corresponding Batteries,” incorporated herein byreference. Compositions in which A is lithium as a dopant forsubstitution for Mn are described in published U.S. patent application2011/0052989A to Venkatachalam et al., entitled “Lithium Doped CathodeMaterial,” incorporated herein by reference. The specific performanceproperties obtained with +2 metal cation dopants, such as Mg⁺², aredescribed in copending U.S. patent application Ser. No. 12/753,312 toKarthikeyan et al., entitled “Doped Positive Electrode Active Materialsand Lithium Ion Secondary Batteries Constructed Therefrom,” incorporatedherein by reference.

If b+α+β+γ+δ is approximately equal to 1, the positive electrodematerial with the formula above can be represented approximately in twocomponent notation as x Li₂M′O₃.(1−x)LiMO₂ where 0<x<1, M is one or moremetal cations with an average valence of +3 within some embodiments atleast one cation being a Mn ion or a Ni ion and where M′ is one or moremetal cations, such as Mn⁺⁴, with an average valence of +4. As notedabove, it is believed that the corresponding material has two distinctphysical phases related to the separate components of the two componentnotation. The multi-phased material is believed to have an integratedlayered-layered composite crystal structure with the excess lithiumsupporting the stability of the composite material. For example, in someembodiments of lithium rich materials, a layered Li₂MnO₃ material may bestructurally integrated with a layered LiMO₂ component where Mrepresents selected non-lithium metal elements or combinations thereof.

Recently, it has been found that the performance properties of thepositive electrode active materials can be engineered around thespecific design of the composition stoichiometry. The positive electrodeactive materials of particular interest can be represented approximatelyin two component notation as x Li₂MnO₃.(1−x) LiMO₂, where M is one ormore metal elements with an average valence of +3 and with one of themetal elements being Mn and with another metal element being Ni and/orCo. In general, 0<x<1, but in some embodiments 0.03≦x≦0.55, in furtherembodiments 0.075≦x≦0.50, in additional embodiments 0.1≦x≦0.4, and inother embodiments 0.125≦x≦0.325. A person of ordinary skill in the artwill recognize that additional ranges within the explicit ranges ofparameter x above are contemplated and are within the presentdisclosure. For example, M can be a combination of nickel, cobalt andmanganese, which, for example, can be in oxidation states Ni⁺², Co⁺³,and Mn⁺⁴ within the initial lithium manganese oxides. The overallformula for these compositions can be written asLi_(2(1+x)/(2+x))Mn_(2x/(2+x))M_((2−2x)/(2+x))O₂. In the overallformula, the total amount of manganese has contributions from bothconstituents listed in the two component notation. Thus, in some sensethe compositions are manganese rich.

In some embodiments, M can be written as Ni_(u)Mn_(v)Co_(w)A_(y). Forembodiments in which y=0, this simplifies to Ni_(u)Mn_(y)Co_(w). If Mincludes Ni, Co, Mn, and optionally A the composition can be writtenalternatively in two component notation and single component notation asthe following.

xLi₂MnO₃.(1−x)LiNi_(u)Mn_(v)Co_(w)A_(y)O₂,  (1)

Li_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O₂,  (2)

with u+v+w+y≈1 and b+α+β+γ+δ≈1. The reconciliation of these two formulasleads to the following relationships:

b=x/(2+x),

α=2u(1−x)/(2+x),

β=2x/(2+x)+2v(1−x)/(2+x),

γ=2w(1−x)/(2+x),

δ=2y(1−x)/(2+x),

and similarly,

x=2b/(1−b),

u=α/(1−3b),

v=(β−2b)/(1−3b),

w=γ/(1−3b),

y=δ/(1−3b).

In some embodiments, it may be desirable to have u≈v, such that Li Ni MnCo_(w) A becomes approximately LiNi_(u)Mn_(u)Co_(w)A_(y)O₂. In thiscomposition, when y=0, the average valence of Ni, Co and Mn is +3, andif u≈v, then these elements can have valences of approximately Ni⁺²,Co⁺³ and Mn⁺⁴ to achieve the average valence. When the lithium ishypothetically fully extracted, all of the elements go to a +4 valence.A balance of Ni and Mn can provide for Mn to remain in a +4 valence asthe material is cycled in the battery. This balance avoids the formationof Mn⁺³, which has been associated with dissolution of Mn into theelectrolyte and a corresponding loss of capacity. However, thisperspective assumes maintenance of the two distinct phases with thephases remaining stable as the battery is cycled, and a more intricateview is described herein. In the partial activation formation protocoldescribed herein, a significant fraction of the lithium remainsfollowing the charge process.

In further embodiments, the composition can be varied around the formulafor the material with balanced amounts of Mn and Ni in the LiMO₂ phaseof the material such that the approximate formula for the material is xLi₂MnO₃.(1−x) LiNi_(u+Δ)Mn_(u−Δ)Co_(w)A_(y)O₂, where the absolute valueof A generally is no more than about 0.3 (i.e., −0.3≦Δ≦0.3), inadditional embodiments no more than about 0.2 (−0.2≦Δ≦0.2) in someembodiments no more than about 0.175 (−0.175≦Δ≦0.175) and in furtherembodiments no more than about 0.15 (−0.15≦Δ≦0.15). With 2u+w+y≈1,desirable ranges of parameters are in some embodiments 0≦w≦1, 0≦u≦0.5,0≦y≦0.1 (with the proviso that both u+Δ and w are not zero), in furtherembodiments, 0.1≦w≦0.6, 0.1≦u≦0.45, 0≦y≦0.075, and in additionalembodiments 0.2≦w≦0.5, 0.2≦u≦0.4, 0≦y≦0.05. A person of ordinary skillin the art will recognize that additional ranges of compositionparameters within the explicit ranges above are contemplated and arewithin the present disclosure. As used herein, the notation(value1≦variable≦value2) implicitly assumes that value 1 and value 2 areapproximate quantities. The engineering of the composition to obtaindesired battery performance properties is described further in the '981application cited above.

In general, various processes can be performed for synthesizing thedesired lithium rich metal oxide materials described herein havingnickel, cobalt, manganese and additional optional metal cations in thecomposition and exhibiting the high specific capacity performance. Inparticular, for example, sol gel, co-precipitation, solid statereactions and vapor phase flow reactions can be used to synthesize thedesired materials. In addition to the high specific capacity, thematerials can exhibit a good tap density which leads to high overallcapacity of the material in fixed volume applications. Specifically,lithium rich metal oxide compositions were used in coated forms togenerate the results in the Examples below.

Specifically, the synthesis methods based on co-precipitation have beenadapted for the synthesis of compositions with the formulaLi_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2−z)F_(z), as described above. In theco-precipitation process, metal salts are dissolved into an aqueoussolvent, such as purified water, with a desired molar ratio. Suitablemetal salts include, for example, metal acetates, metal sulfates, metalnitrates, and combination thereof. The concentration of the solution isgenerally selected between 1M and 3M. The relative molar quantities ofmetal salts can be selected based on the desired formula for the productmaterials. Similarly, the dopant elements can be introduced along withthe other metal salts at the appropriate molar quantity such that thedopant is incorporated into the precipitated material. The pH of thesolution can then be adjusted, such as with the addition of Na₂CO₃and/or ammonium hydroxide, to precipitate a metal hydroxide or carbonatewith the desired amounts of metal elements. Generally, the pH can beadjusted to a value between about 6.0 to about 12.0. The solution can beheated and stirred to facilitate the precipitation of the hydroxide orcarbonate. The precipitated metal hydroxide or carbonate can then beseparated from the solution, washed and dried to form a powder prior tofurther processing. For example, drying can be performed in an oven atabout 110° C. for about 4 to about 12 hours. A person of ordinary skillin the art will recognize that additional ranges of process parameterswithin the explicit ranges above are contemplated and are within thepresent disclosure.

The collected metal hydroxide or carbonate powder can then be subjectedto a heat treatment to convert the hydroxide or carbonate composition tothe corresponding oxide composition with the elimination of water orcarbon dioxide. Generally, the heat treatment can be performed in anoven, furnace or the like. The heat treatment can be performed in aninert atmosphere or an atmosphere with oxygen present. In someembodiments, the material can be heated to a temperature of at leastabout 350° C. and in some embodiments from about 400° C. to about 800°C. to convert the hydroxide or carbonate to an oxide. The heat treatmentgenerally can be performed for at least about 15 minutes, in furtherembodiments from about 30 minutes to 24 hours or longer, and inadditional embodiments from about 45 minutes to about 15 hours. Afurther heat treatment can be performed at a second higher temperatureto improve the crystallinity of the product material. This calcinationstep for forming the crystalline product generally is performed attemperatures of at least about 650° C., and in some embodiments fromabout 700° C. to about 1200° C., and in further embodiments from about700° C. to about 1100° C. The calcination step to improve the structuralproperties of the powder generally can be performed for at least about15 minutes, in further embodiments from about 20 minutes to about 30hours or longer, and in other embodiments from about 1 hour to about 36hours. The heating steps can be combined, if desired, with appropriateramping of the temperature to yield desired materials. A person ofordinary skill in the art will recognize that additional ranges oftemperatures and times within the explicit ranges above are contemplatedand are within the present disclosure.

The lithium element can be incorporated into the material at one or moreselected steps in the process. For example, a lithium salt can beincorporated into the solution prior to or upon performing theprecipitation step through the addition of a hydrated lithium salt. Inthis approach, the lithium species is incorporated into the hydroxide orcarbonate material in the same way as the other metals. Also, due to theproperties of lithium, the lithium element can be incorporated into thematerial in a solid state reaction without adversely affecting theresulting properties of the product composition. Thus, for example, anappropriate amount of lithium source generally as a powder, such asLiOH.H₂O, LiOH, Li₂CO₃, or a combination thereof, can be mixed with theprecipitated metal carbonate or metal hydroxide. The powder mixture isthen advanced through the heating step(s) to form the oxide and then thecrystalline final product material.

Further details of the hydroxide co-precipitation process are describedin published U.S. patent application 2010/0086853A (the '853application) to Venkatachalam et al. entitled “Positive ElectrodeMaterial for Lithium Ion Batteries Having a High Specific DischargeCapacity and Processes for the Synthesis of these Materials”,incorporated herein by reference. Further details of the carbonateco-precipitation process are described in published U.S. patentapplication 2010/0151332A (the '332 application) to Lopez et al.entitled “Positive Electrode Materials for High Discharge CapacityLithium Ion Batteries”, both incorporated herein by reference.

Coatings and Formation of Coatings on Positive Electrode ActiveMaterials

Inorganic coatings, such as metal halide coatings and metal oxidecoatings, on lithium rich positive electrode active materials have beenfound to significantly improve the performance of the resulting lithiumion batteries, although the coatings are believed to be inert withrespect to battery cycling. Additionally, the specific capacity of thebatteries also shows desirable properties with the coatings, and theirreversible capacity loss of the first cycle of the battery can bereduced in some embodiments. If the coating is properly designed, thecoated materials can maintain desirable rate capability. Theseperformance improvements can be similarly exploited in the improvedcycling described herein.

With respect to metal oxide and metal halide coatings, a coating with acombination of metal and/or metalloid elements can be used for thecoating compositions. Suitable metals and metalloid elements for thefluoride coatings include, for example, Al, Bi, Ga, Ge, In, Mg, Pb, Si,Sn, Ti, Tl, Zn, Zr and combinations thereof. Aluminum fluoride can be adesirable coating material since it has a reasonable cost and isconsidered environmentally benign. Metal fluoride coatings are describedgenerally in published PCT application WO 2006/109930A to Sun et al.,entitled “Cathode Active Materials Coated with Fluorine Compound forLithium Secondary Batteries and Method for Preparing the Same,”incorporated herein by reference. It has been found that metal/metalloidfluoride coatings can significantly improve the performance of lithiumrich layered compositions for lithium ion secondary batteries. See, forexample, the '853 application and the '332 application cited above, aswell as published U.S. patent application number 2011/0111298 (the '298application) to Lopez et al., entitled “Coated Positive ElectrodeMaterials For Lithium Ion Batteries,” incorporated herein by reference.Desirable performance results for non-fluoride metal halide coatingshave been described in published U.S. patent application 2012/0070725 toVenkatachalam et al., entitled “Metal Halide Coatings on Lithium IonBattery Positive Electrode Materials and Corresponding Batteries,”incorporated herein by reference. This patent application also discussesmethods for formation of desired metal halide coatings.

An increase in capacity and a reduction in irreversible capacity losswere noted with Al₂O₃ coatings by Wu et al., “High Capacity,Surface-Modified Layered Li[Li_((1−x/3)Mn_((2−x)/3)Ni_(x/3)Co_(x/3)]O₂Cathodes with Low Irreversible Capacity Loss,” Electrochemical and SolidState Letters, 9 (5) A221-A224 (2006), incorporated herein by reference.The use of a LiNiPO₄ coating to obtain improved cycling performance isdescribed in an article to Kang et al. “Enhancing the rate capability ofhigh capacity xLi₂MnO₃ (1−x)LiMO₂ (M=Mn, Ni, Co) electrodes by Li—Ni—PO₄treatment,” Electrochemistry Communications 11, 748-751 (2009),incorporated herein by reference, and this article can be referencedgenerally with respect to the formation of metal phosphate coatings.Desirable properties of metal oxide coatings on lithium rich positiveelectrode active materials are described further in published U.S.patent application 2011/0076556A to Karthikeyan et al., entitled “MetalOxide Coated Positive electrode Materials for Lithium-Based Batteries,”incorporated herein by reference.

In some embodiments, the coating improves the specific capacity of thebatteries even though the coating itself is not electrochemicallyactive. However, the coatings also influence other properties of theactive material, such as the average voltage, thermal stability andimpedance. The selection of the coating properties can incorporateadditional factors related to the overall range of properties of thematerial.

In general, the coatings can have an average thickness of no more than25 nm, in some embodiments from about 0.5 nm to about 20 nm, in otherembodiments from about 1 nm to about 12 nm, in further embodiments from1.25 nm to about 10 nm and in additional embodiments from about 1.5 nmto about 8 nm. A person of ordinary skill in the art will recognize thatadditional ranges of coating material within the explicit ranges aboveare contemplated and are within the present disclosure. The amount ofcoating materials to achieve desired improvement in battery performancecan be related to the particle size and surface area of the uncoatedmaterial. Further discussion of the effects of coating thickness on theperformance properties for coated lithium rich lithium metal oxides isfound in the '298 application cited above.

A metal fluoride coating can be deposited using a solution basedprecipitation approach. A powder of the positive electrode material canbe mixed in a suitable solvent, such as an aqueous solvent. A solublecomposition of the desired metal/metalloid can be dissolved in thesolvent. Then, NH₄F can be gradually added to the dispersion/solution toprecipitate the metal fluoride. The total amount of coating reactantscan be selected to form the desired thickness of coating, and the ratioof coating reactants can be based on the stoichiometry of the coatingmaterial. The coating mixture can be heated during the coating processto reasonable temperatures, such as in the range from about 60° C. toabout 100° C. for aqueous solutions from about 20 minutes to about 48hours, to facilitate the coating process. After removing the coatedelectroactive material from the solution, the material can be dried andheated to temperatures generally from about 250° C. to about 600° C. forabout 20 minutes to about 48 hours to complete the formation of thecoated material. The heating can be performed under a nitrogenatmosphere or other substantially oxygen free atmosphere.

An oxide coating is generally formed through the deposition of aprecursor coating onto the powder of active material. The precursorcoating is then heated to form the metal oxide coating. Suitableprecursor coating can comprise corresponding metal hydroxides, metalcarbonates or metal nitrates. The metal hydroxides and metal carbonateprecursor coating can be deposited through a precipitation process sincethe addition of ammonium hydroxide and/or ammonium carbonate can be usedto precipitate the corresponding precursor coatings. A metal nitrateprecursor coating can be deposited through the mixing of the activecathode powder with a metal nitrate solution and then evaporating thesolution to dryness to form the metal nitrate precursor coating. Thepowder with a precursor coating can be heated to decompose the coatingfor the formation of the corresponding metal oxide coating. For example,a metal hydroxide or metal carbonate precursor coating can be heated toa temperature from about 300° C. to about 800° C. for generally fromabout 1 hr to about 20 hrs. Also, a metal nitrate precursor coatinggenerally can be heated to decompose the coating at a temperature fromabout 250° C. to about 550° C. for at least about 30 minutes. A personof ordinary skill in the art can adjust these processing conditionsbased on the disclosure herein for a specific precursor coatingcomposition.

Formation Protocol with Partial Activation

The formation protocol described herein has been found to provide a morestable battery structure following the completion of initialirreversible changes to the battery during the first charge of thebattery. The formation protocol comprises three steps, an initial chargestep, a rest period under an open circuit and a subsequent charge stepto a selected partial activation voltage. The formation protocol can bedesigned with additional charge steps and/or rest steps, if desired. Theselected second charge voltage is selected to provide for a desireddegree of partial activation of the positive electrode active materialto achieve a desired specific capacity while providing for excellentstability with cycling. In comparison with a multiple step formationcycle with full activation significantly over 4.4V, evidence suggests ashorter rest period can be used to form the battery while providing foroutstanding cycling of the battery, although the reasons for thisdifference is not presently understood. While the multiple stepformation protocol with partial activation can be effectively used forthe range of lithium enriched cathode active materials, the formationprotocol is particularly effective to stabilize cycling for compositionswith moderate lithium enrichment. In particular, for active compositionswith x in Eq. 1 above of no more than about 0.325, partial activationwith the multiple step protocol has been found to result in a batterymaterial with excellent cycling out to thousands of charge/dischargecycles with relatively high specific capacities and excellent ratecapability. In particular, for lithium enrichment corresponding to aboutx<0.325, the positive electrode active material exhibits partialactivation at a charge voltage of about 4.275V to about 4.39V with nosignificant further activation with cycling with a charge voltage at thepartial activation voltage.

During the first cycle of a battery, the battery is prepared forsubsequent cycling. In particular, it is believed that the batteryelectrodes undergo irreversible changes to the materials in the firstcycle that can affect the performance characteristics of a battery. Inlight of these changes, the first charge/discharge cycle can be referredto as the formation or activation cycle, and the procedure for the firstcycle can be referred to as the formation of the cell. For example, itis believed that during the formation cycle of a battery, compositionsin the battery, e.g., a solvent composition and the electrolyte salt,can decompose and deposit on the negative electrode during charging andform a layer of material known as a solid electrolyte interphase (SEI)layer. If the resulting SEI layer is effectively stable, the SEI layercan reduce further electrolyte decomposition on subsequent chargingcycles of the battery. On the other hand, where the SEI layer is notstably formed, successive charge cycles may further irreversibly consumethe battery electrolyte material or a component thereof, and thedecomposition of the electrolyte can lead to a shortened battery cyclelifetime.

For the lithium rich materials described herein, the positive electrodeactive materials also generally undergo irreversible changes during thefirst charge of the battery. These irreversible changes can contributeto the irreversible capacity loss of the battery, which can be greaterthan the irreversible capacity loss attributable to the SEI layer. Ithas been found that coating the lithium rich materials can result in adecrease in the irreversible capacity loss, presumably related to theirreversible changes to the positive electrode active material.Nevertheless, significant irreversible changes occur in relationshipwith the lithium rich composition, and the loss of molecular oxygen hasbeen observed in this context. The two step partial activation protocolhas been discovered to result in a decrease in the oxygen loss duringthe formation cycle as well as to greatly stabilize the material forcycling.

The multistep partial activation protocol described herein provides forimproved stability of the resulting battery for cycling. The firstcharge step is believed to induce initial irreversible changes to thebattery. In particular, the first charge can be performed to a voltagefrom about 2.1 V to about 4.225V, in further embodiments from about 2.5Vto about 4.22V and in additional embodiments from about 2.75V to about4.215V. The examples below demonstrate that for the electrolytesdescribed herein, the electrolyte undergoes reduction at batterypotentials above about 2.1V when the SEI layer is essentially formed inassociation with the anode active material. Thus, an initial charge to abattery voltage of at least about 2.1V can form the SEI layer during afirst charge step. The initially charged battery can be stored in anopen circuit voltage for a period of time, also referred to as restperiod or aging, generally at least about 6 hours, in furtherembodiments from about 8 hours to about 8 days and in other embodiments,from about 10 hours to about 6 days. In general, the battery can bestored at a temperature from about 20° C. to about 75° C. In someembodiments, the rest period can be performed at room temperature, i.e.,from 22° C. to 25° C. After the rest period, the partial activationcharge can be performed to a voltage from about 4.275V to about 4.39V,in further embodiments from about 4.28V to about 4.38V and in additionalembodiments from about 4.3V to about 4.365V. A person of ordinary skillin the art will recognize that additional ranges of rest parameters andvoltage for the charges within the explicit ranges above arecontemplated and are within the present disclosure.

As noted above, charging to a higher voltage is believed to activatehigher voltage phases of the positive electrode active material to makethese phases available for cycling. Some irreversible changes to thematerial may take place during this activation. The formation protocoldescribed herein is designed to performed what is termed partialactivation, which can be considered activation to voltages of no morethan about 4.39V. With partial activation, significant availablespecific capacity of the positive electrode active material is notaccessed during cycling. The charge voltage during cycling is generallyno more than the partial activation voltage during the formation cycle.In the partial formation process, the activation of the positiveelectrode active material evidently substantially avoids formation ofphases that are unstable with cycling so that very long term cyclingstability can be achieved. For lower values of lithium enrichment,further activation does not take place during cycling of the batteriesto charge voltages of no more than about 4.39V. However, for batteriesformed with materials having a greater lithium enrichment of roughlyx>0.3, the batteries can exhibit some additional gradual activationduring cycling to a charge voltage of roughly 4.39V or greater. Somegradual activation may or may not be desirable depending on the overallstability of the capacity over sufficiently long term cycling of thebattery.

The charging of the battery generally is performed through theapplication of a suitable voltage across the poles of the battery. Thecharging can be controlled in appropriate ways. For example, the chargesteps can comprises, for example, constant current (CC) charging,constant voltage (CV) charging, and mixed charging methods. During a CCcharging process, a battery is charged to the selected voltage value byintroducing an approximately constant current through the battery untilthe selected voltage value is reached. In a CV charging process, abattery can be charged to the selected voltage value by applying aconstant voltage across the battery until the open circuit voltagereaches the selected voltage value and/or until a selected cut off ofinduced current is reached with the induced current gradually decreasingand/or a selected period of time has passed. In general, the particularcharging steps can be divided, if desired, into multiple steps withdifferent constant currents and/or constant voltages used for therespective steps. For example, a constant current can be used for aportion of a charge step and a constant voltage can be used for anotherpart of the charge step.

In general, the initial lower voltage charge can be performed under aconstant current charge, a constant voltage charge or a combinationthereof. Regardless of the charging approach, the parameters of thecharge can be adjusted such that the overall rate of performing thischarge is at least about 30 minutes, in further embodiments for at leastabout 45 minutes, in additional embodiments from about 1.0 hours toabout 12 hours and in other embodiments from about 1.5 hours to about 8hours. A person of ordinary skill in the art will recognize thatadditional charge rate ranges within the explicit ranges above arecontemplated and are within the present disclosure.

Following the initial charge to the first selected voltage, it has beendiscovered that significantly improved cycling results can be obtainedwhen the first charge/discharge cycle described herein comprises a restperiod wherein a battery is held in an open circuit configuration for aparticular duration. In an open circuit configuration, no charge flowsbetween the poles of the battery. During this storage or rest period,further formation of the SEI layer may take place or other stabilizingchanges may take place within the battery, although we do not wish to belimited by theory. If the SEI layer does become thicker with a longerrest period, the observation that the performance peaks as a function ofrest period suggests that lithium movement through the SEI layer can berestricted if the SEI layer is too thick. Also, an SEI layer that isthicker than desirable may contribute dead weight to the battery. Sincethe selected voltage generally is appropriately selected, the formationof the SEI layer and/or other formation processes can take place underappropriate low voltage situations without undesirable irreversiblechanges that have been observed to take place at high voltages for theinitial charge.

For a multistep formation protocol with full activation as described inthe '751 application, evidence was presented that a longer rest periodleads to a more stable and possibly thicker SEI layer. Specifically,based on differential scanning calorimeter measurements on the negativeelectrodes after formation indicated that the negative electrodecomposition did not undergo decomposition until higher temperatures ifthe SEI layer was formed over a longer open circuit rest period. Thestability temperature was taken as the onset temperature, where theonset temperature is obtained by drawing a tangent through theinflection point along the leading edge of a peak of the DSC curve, andthe onset temperature is the temperature at which the tangent lineintersects the baseline that reflects the heat capacity of the material.Also, the tip or highest point of a peak in the DSC plot can provideanother reference point. A peak generally indicates a change, e.g.,decomposition, in the SEI layer associated with the negative electrodematerial. It is expected that more stabile SEI layers also result fromthe rest period during the multistep partial activation formationprotocol described herein.

A subsequent charge step of a first charge/discharge cycle generallycomprises charging a battery to a terminal voltage value that is atleast as great as the specified fully charged cycling voltage of thebattery, which generally follows the rest period. During the subsequentcharge step, the battery is further activated with respect to increasingthe capacity due to incorporation of additional lithium into thenegative electrode active material. This voltage for the subsequentcharge step is greater than the initial charge of the first chargecycle. Additionally, the terminal voltage in the partial activationformation protocol avoids overcharge conditions wherein a batteryundergoes undesirable irreversible processes and possibly dangerousinstabilities.

In general, while two charge steps are described herein to bring thebattery up to a selected partial activation voltage, additional chargesteps can be used to bring the battery up to the selected voltage forthe first cycle. For example, three, four or more charging steps can beused to step the voltage up to the voltage for full activation. Theseadditional steps can be used before the rest step, after the rest stepor a combination thereof. However, if greater than two charge steps areused, one or a plurality of these charge steps generally combine toreproduce the conditions described above for the initial charge stepwith a rest prior to charge to the full cycling voltage. If a pluralityof rest steps is used between charging steps, the rest steps may or maynot be performed at the same temperature. Similarly, a rest step may notbe performed at a constant temperature through the rest step, and thereference to a temperature of a rest step is considered the approximateaverage temperature unless indicated otherwise.

In some embodiments of the formation cycle, the initial charge cancomprises a constant current charge to the selected initial chargevoltage, which is followed after the rest period by the constant voltageformation step. A subsequent constant voltage charge step can beperformed until the induced current falls below a selected cut offvalue, and such a charge generally can involve significant current flowat an open circuit voltage approximately equal to the constant chargevoltage. In a constant current charging step of the formation cycle, thebattery can be charged at a current from about C/40 to about 5 C, inother embodiments from about C/20 to about 3 C and in furtherembodiments from about C/15 to about 2 C, until a selected voltage valueis reached. A person of ordinary skill in the art will recognize thatadditional ranges of current within the explicit ranges above arecontemplated and are within the present disclosure. The subsequentcharging step to activate the battery can be performed using a constantvoltage charge, although a constant current can be used in principle.Use of the multiple step formation procedure described herein canimprove the cycle life of high voltage lithium ion batteries.

After the activation charge, the battery is discharged to complete thefirst charge/discharge cycle. For example, the battery can be dischargedrelatively deeply to a voltage of 2 volts. In some embodiments, thebattery is discharged to a voltage below 2.75 volts, in otherembodiments to a voltage from 1.5 volts to 2.65 volts, in additionalembodiments from about 1.75 to about 2.6 volts and in furtherembodiments from about 1.8 volts to about 2.5 volts. A person ofordinary skill in the art will recognize that additional ranges ofdischarge voltages within the explicit ranges above are contemplated andare within the present disclosure. The battery generally is then chargedagain when ready for use. The battery can be partially charged to aselected voltage for distribution.

Battery Performance

The multiple step partial activation formation protocol described hereincan be effectively used to improve battery performance in meaningfulways that are significant for commercial use. The partial activationprotocols can be used in conjunction with cycling over correspondingvoltage windows to achieve outstanding long term cycling of thebatteries, as described in the '590 application. As shown herein, theimproved formation protocol provides for decreased positive electrodeinstability as determined by decrease transition metal dissolution, animprovement in the rate capability even though capacity of the activematerial is not accessed, a decrease in the DC resistance and animprovement in the calendar life. The improved performance of thebatteries is particularly significant for application to vehiclepropulsion.

It has been found that positive electrode instability can result in thedecomposition of the metal oxide in the cathode, and in particularmanganese ions can elute from the metal oxide if unstable phases areformed cycling. The transition metal that elute from the metal oxideinto the electrolyte can diffuse then to the negative electrode wherethe metal ions can be deposited. The direct correlation of manganesemigration to the negative electrode with depletion of metal from thepositive electrode active material and development of pores in thepositive electrode active material as a result of cycling has beendescribed in published U.S. patent application 2012/0107680 to Amiruddinet al., entitled “Lithium Ion Batteries With Supplemental Lithium,”incorporated herein by reference. The stability of the positiveelectrode following activation has been found to be much more stableusing the multiple step partial activation formation protocol asevaluated by manganese dissolution. Specifically, after the secondcharge, following a zero time rest period, to 4.35V or to 4.6V at a rateof C/10, the batteries are stored for a week at 100% state of charge.The batteries are then fully discharged and disassembled to remove theanode. The anodes are then analyzed for metal content using inductivelycoupled plasma analysis. Using the multiple step partial formationprotocol with a final charge to 4.35V, the manganese dissolution asdetermined by a measurement of metal in the anode can be no more thanabout 150 parts per million by weight (ppm), in further embodiments nomore than about 135 ppm and in other embodiments from about 50 ppm toabout 125 ppm by weight. In addition, the total amount of Mn, Co and Nimetal in the anode after 600 cycles from 4.35V to 2V can be no more thanabout 200 ppm by weight, in further embodiments no more than about 175ppm, and in other embodiments from about 75 ppm to about 150 ppm byweight. A person of ordinary skill in the art will recognize thatadditional ranges of amounts of metal dissolution into the anode withinthe explicit ranges above are contemplated and are within the presentdisclosure.

With the partial activation of the positive electrode active material,lithium is left in the material at the charge voltage, which is apurposeful abandonment of some of the battery capacity in exchange forincreased stability of the material. As the discharge rate is increased,the specific capacity of the lithium rich metal oxides decreases, whichpresumably is due to internal resistance in the material to lithiumextraction from the material. It has been surprisingly discovered thatthe positive electrode active materials formed with the partialactivation formation protocol can be formed into a battery that exhibitsa significantly reduced decrease of capacity with increasing dischargerates relative to battery that is activated to a full activationvoltage. For at least certain compositions, the battery activated withthe multiple step partial formation can actually exhibit a higherspecific capacity at high discharge rates, e.g., 2 C, than acorresponding battery formed with full activation to 4.6V. For example,the positive electrode active material can exhibit a specific dischargecapacity from 4.35V to 2V at a rate of 2 C of at least about 140 mA, infurther embodiments at least about 145 mAh/g and in additionalembodiments from about 146 mAh/g to about 160 mAh/g. This ratecapability can also be expressed as a smaller decrease in specificcapacity with increasing rate, which tends to more directly reflect therate capability with less influence from the particular stoichiometry ofthe material that can influence the numerical value of the specificcapacity. Thus, the specific discharge capacity at a rate of 2 C from4.35V to 2V can be at least about 87.5% of the specific dischargecapacity at a rate of C/5 from 4.35V to 2V, in further embodiments atleast about 88.5% and in other embodiments from about 89% to about 92.5%of the specific discharge capacity at a rate of C/5 from 4.35V to 2V. Aperson of ordinary skill in the art will recognize that additionalranges of specific capacity and relative specific capacities within theexplicit ranges above are contemplated and are within the presentdisclosure.

It is also useful to evaluate the DC resistance profiles as a functionof state of charge. In the Examples below, the DC resistance isevaluated for pouch batteries formed with a single cathode layer and asingle anode layer, so the batteries are not designed for low impedanceperformance suitable for vehicle applications. Nevertheless, therelative values provide useful information of the effect on electricalresistance as a result of the formation protocols. The DC resistance ismeasured after the battery rests for an hour at the particular state ofcharge, and a short pulse is applied. The DC resistance then is definedas the change in voltage from the beginning of the pulse to the end ofthe pulse divided by the change in current at the beginning of the pulseand at the end of the pulse. In the Examples, a 17 second 5 C pulse isused for the evaluation of power in larger capacity pouch batteries. Incomparison with a fully activation formation protocol, the multiple steppartial activation formation protocol results in a decrease inelectrical resistance in the battery of greater than about 10% across astate of charge from 10% to 90%.

The DC resistance directly influences the power output at thecorresponding state of charge. Two different power values are calculatedfrom the pulse measurements. A discharge power is defined as V_(min)(V_(ocv)−V_(min))/R, where V_(min) is the lowest voltage during thepulse and V_(ocv) is the open circuit voltage. The lower state of chargevalues are particularly significant for determining the operating stateof charge for the battery in use. A regen power is defined as V_(max)(V_(max)−V_(ocv))/R, where V_(max) is the maximum voltage during theapplication of the pulse. The regen power is generally considered asmore significant at higher state of charge. With the partial activationformation protocol, the batteries surprisingly have greater dischargepower at low states of charge even though the lower charge voltage wouldtend to lower the battery voltage. While the regen powers are lower forthe partial activation formation protocol relative to the powers forbatteries that are fully activated to 4.6V, the regen powers obtainedfor the batteries for the multiple step partial activation formationprotocol are generally within acceptable ranges for vehicleapplications.

With respect to the performance of partially activated batteries, thecapacity may or may not increase with cycling over a moderate number ofcycles as the battery continues gradual activation. With adjustment ofthe partial activation voltage and the cycling voltage, extremely flatcapacities can be obtained out to several thousands of cycles. Thus,batteries with partial activation can exhibit a capacity retentioncorresponding to a capacity at the 500th discharge cycle that is atleast about 90%, in further embodiments at least about 92.5% in otherembodiments at least about 95%, in additional embodiments at least about97.5% relative to the 5th cycle discharge capacity when discharged at arate of C/3 from 4.25V to 2.0V. Similarly, the batteries can exhibit acapacity retention corresponding to a capacity at the 1000th dischargecycle that is at least about 87.5%, in further embodiments at leastabout 90%, in additional embodiments at least about 92.5% and in otherembodiments at least about 95% relative to the 5th cycle dischargecapacity when discharged at a rate of 2 C from 4.25V to 2.0V. Also, thebatteries can exhibit a capacity retention corresponding to a capacityat the 2500th discharge cycle that is at least about 87%, in furtherembodiments at least about 90%, and in other embodiments at least about92.5% relative to the 5th cycle discharge capacity when discharged at arate of 2 C from 4.25V to 2.0V. Furthermore, a battery with partialactivation discharged from 4.25V to 2.0V can exhibit at least about87.5% at 500 cycles of the 5th cycle average voltage, in additionalembodiments at least about 90%, in other embodiments at least about92.5% and in further embodiments at least about 95% when discharged at arate of C/3. Similarly, a battery with partial activation dischargedfrom 4.25V to 2.0V can exhibit at least about 85% at 1000 cycles of the5th cycle average voltage, in additional embodiments at least about 90%and in further embodiments at least about 95% when discharged at a rateof 2 C. Also, a battery with partial activation discharged from 4.25V to2.0V can exhibit at least about 85% at 2500 cycles of the 5th cycleaverage voltage, in additional embodiments at least about 90% and infurther embodiments at least about 95% when discharged at a rate of 2 C.A person of ordinary skill in the art will recognize that additionalranges of performance of batteries with partial activation within theexplicit ranges above are contemplated and are within the presentdisclosure.

As shown herein, the batteries can also be cycled from 4.35V to 2V withoutstanding cycling stability. Thus, the batteries can exhibit acoulombic efficiency corresponding with a discharge capacity at the200th cycle at least about 97% of the 10th cycle discharge capacity, infurther embodiments at least about 98% and in additional embodiments atleast about 98.5% of the 10th cycle discharge capacity when cycledbetween 4.35V and 2V at a rate of 1 C at room temperature. When cycledat 45° C., the batteries can exhibit a coulombic efficiencycorresponding with a discharge capacity at the 200th cycle at leastabout 96% of the 10th cycle discharge capacity, in further embodimentsat least about 97% and in additional embodiments at least about 98% ofthe 10th cycle discharge capacity when cycled between 4.35V and 2V at arate of 1 C. A person or ordinary skill in the art will recognize thatadditional ranges of coulombic efficiency within the explicit rangesabove at 200 cycles are contemplated and are within the presentdisclosure.

The improvements in desired performance parameters for the positiveelectrode active material can be combined with corresponding improvedbattery designs to provide significant improvements in batteryperformance, especially for pouch batteries with a stack of electrodesthat have relatively low proportion of weight and volume contributionsfrom container materials. With carbon based negative electrode activematerials, the lithium ion secondary battery can have a discharge energydensity of at least about 150 Wh/kg at a discharge rate of C/3 from4.35V to 2V, in further embodiments at least about 160 Wh/kg and inadditional embodiments from about 180 Wh/kg to about 230 Wh/kg at adischarge rate of C/3 from 4.35V to 2V. Also, the battery can have avolumetric energy density of at least about 300 Wh/l (watt hours/liter),in further embodiments at least about 310 Wh/l and in additionalembodiments from about 320 Wh/l to about 400Wh/l. A person of ordinaryskill in the art will recognize that additional ranges of energy densitywithin the specific ranges above are contemplated and are within thepresent disclosure.

Also, the batteries formed with the multiple step partial activationformation protocol exhibit improved calendar life. The calendar lifereflects how long a battery can be stored without an unacceptable dropin battery performance. Specifically, calendar life can be testedthrough storage of the battery in an open circuit at a specifictemperature. A higher temperature storage test can be used to acceleratethe calendar life evaluation. The evaluation of storage life at multipletemperatures can facilitate extrapolation of calendar life predictions.To perform the test, the battery is prepared with the first formationcycle and then charged to an 80% state of charge for storage, althoughalternative procedures can be used based on 100% state of charge, 60%state of charge or other selected value. Periodically, such as everymonth, the batteries are cycled once to determine the battery capacity,and then returned to an 80% state of charge for continued storage.

An end of calendar life can be set at a time at which the capacity ofthe battery drops a certain amount below the initial battery capacity.For vehicle battery applications, a target end of calendar life can beset when the battery capacity falls more than 20% below the initialbattery capacity after 5 years of storage at room temperature, althougha cutoff of 30% capacity loss can be used if desired and also a longertime period, such as 10 years, can similarly be used if desired. Also,the storage results at one year can be considered and extrapolatedappropriately. Reasonable extrapolation can be based on appropriatetrends in the capacity drop, such as a linear extrapolation for a lineardecay. However, the permanent capacity loss measurements over the courseof a year may not be linear, so only a portion of the time plot closerto the one year date can be used to obtain an appropriate extrapolation.A person of ordinary skill in the art will recognize that additionalranges of calendar life within the explicit ranges above arecontemplated and are within the present disclosure.

EXAMPLES

Batteries constructed with selected HCMR™ positive electrodecompositions were activated under one of three different formationprotocols. In particular, pouch cell batteries with HCMR™ positiveelectrode and the graphite negative electrode were assembled and tested.The batteries were cycled under different formation protocols and theindividual examples below describe the activation protocols and thecorresponding performance results from the batteries.

The examples below in general use lithium rich HCMR™ lithium metaloxides that are approximately described generally above and specificallyin Example 1 below. The HCMR™ lithium metal oxides are also generallyreferred to as the high capacity positive electrode material. Positiveelectrodes were formed from the high capacity positive electrodematerial powders by initially mixing it thoroughly with conductingcarbon black (Super P™ from Timcal, Ltd, Switzerland) and graphite (KS6™ from Timcal, Ltd). Separately, Polyvinylidene fluoride PVDF (KF1300™from Kureha Corp., Japan) was mixed with N-methyl-pyrrolidone(Sigma-Aldrich) and stirred overnight to form a PVDF-NMP solution. Thehomogeneous powder mixture was then added to the PVDF-NMP solution andmixed for about 2 hours to form a homogeneous slurry. The slurry wasapplied onto an aluminum foil current collector to form a thin, wet filmand the laminated current collector was dried in vacuum oven at 110° C.for about two hours to remove NMP. The laminated current collector wasthen pressed between rollers of a sheet mill to obtain a desiredlamination thickness. The dried positive electrode comprised at leastabout 75 weight percent active metal oxide, at least about 1 weightpercent graphite, and at least about 2 weight percent polymer binder.

A negative electrode was formed from graphitic carbon or elementallithium. The graphitic carbon based negative electrodes comprised atleast about 75 weight percent graphite and at least about 1 weightpercent acetylene black with the remaining portion of the negativeelectrode being polymer binder. The acetylene black was initially mixedwith NMP solvent to form a uniform dispersion. The graphite and polymerwere added to the dispersion to form a slurry. The slurry was applied asa thin-film to a copper foil current collector. A negative electrode wasformed by drying the copper foil current collector with the thin wetfilm in vacuum oven at 110° C. for about two hours to remove NMP. Thenegative electrode material was pressed between rollers of a sheet millto obtain a negative electrode with desired thickness. Elemental lithiumnegative electrodes were formed from lithium foil (FMC Lithium) havingthickness of 125-150 microns.

An electrolyte was selected to be stable at high voltages, andappropriate electrolytes are described in published U.S. patentapplication 2011/0136019 to Amiruddin et al., entitled “Lithium IonBattery With High Voltage Electrolytes and Additives,” incorporatedherein by reference.

For batteries with the lithium foil counter electrodes, the electrodeswere placed inside an argon filled glove box for the fabrication of thecoin cell batteries. Lithium foil (FMC Lithium) having thickness ofroughly 125 micron was used as a negative electrode. A trilayer(polypropylene/polyethylene/polypropylene) micro-porous separator (2320from Celgard, LLC, NC, USA) soaked with electrolyte was placed betweenthe positive electrode and the negative electrode. A few additionaldrops of electrolyte were added between the electrodes.

For a first set of experiments, the electrodes were then sealed inside a2032 coin cell hardware (Hohsen Corp., Japan) using a crimping processto form a coin cell battery. The resulting coin cell batteries weretested with a Maccor cycle tester to obtain charge-discharge curve andcycling stability over a number of cycles. Coin cell batteries withgraphite carbon as negative electrode were formed following similarprocedures.

Pouch cell batteries were constructed with N+1 negative electrode platesalternating with N positive electrode plates such that a negativeelectrode plate was positioned at both ends of the stack, such as 22negative electrode plates and 21 positive electrode plates, althoughdifferent number of electrode plates can be used to form pouch cellbatteries of different energy output based on cell design. Positiveelectrodes were formed as described above with the current collectorcoated on both sides and with a portion of the aluminum currentcollector left uncoated to serve as tab attachment points. Graphiticcarbon electrode is used as negative electrode. In general, the negativeelectrodes have a surface area of about 3.1 cm×4.35 cm and the positiveelectrodes had a surface area of about 3 cm×4.25 cm. The positive andnegative electrodes were alternately stacked and a single trilayer(polypropylene/polyethylene/polypropylene) micro-porous separator (2320from Celgard, LLC, NC, USA) was folded in a Z-pattern with anappropriate electrode in each fold and a negative electrode at thesurface of the folded structure so that a negative electrode is locatedat the ends of the stacks. Nickel and aluminum tabs were then attachedto the negative and positive electrodes, respectively, and the stack wasplaced in a pouch bag and sealed at three edges. Electrolyte was thenadded to the stack through the fourth, open edge and the fourth edge wasthen sealed.

Example 1 Synthesis of Cathode Materials and Corresponding Electrodesand Batteries

High capacity cathode materials represented by formula x Li₂MnO₃.(1−x)LiNi_(u)Mn_(v)Co_(w)Mg_(y)O₂, were synthesized using a proceduredisclosed in published U.S. patent application 2010/0086853A (the '853application) to Venkatachalam et al. entitled “Positive ElectrodeMaterial for Lithium Ion Batteries Having a High Specific DischargeCapacity and Processes for the Synthesis of these Materials”, andpublished U.S. patent application 2010/0151332A (the '332 application)to Lopez et al. entitled “Positive Electrode Materials for HighDischarge Capacity Lithium Ion Batteries”, both incorporated herein byreference. The stoichiometry of cathode materials having compositions1-2 are outlined in Table 1 below.

TABLE 1 Mn (% transition Composition X Mg metals) 1 0.175 0 0.45 2 0.30.01 0.51

Compositions 1 to 2 were then used to construct corresponding positiveelectrodes, which were in turn used to construct corresponding sets ofbatteries with lithium metal counter electrodes using the procedureoutlined above. Additionally, pouch cell batteries were constructedusing the corresponding compositions 1 or 2 above against graphiticcarbon counter electrode using the procedure outlined above. In general,three battery formation protocols outlined in Table 2 below were used toactivate the batteries, and the results are presented in the followingexamples. Unless otherwise indicated, the formation protocols wereperformed with a seven day rest period between the first and secondcharge steps.

TABLE 2 Formation protocol 1st cycle (Max Voltage) Other terms used 14.6 V Full activation 2 4.35 V  Partial activation 3 4.3 V Partialactivation

All of the synthesized materials were coated with an aluminum halidestabilizing coating.

Example 2 Evaluation of Battery Performance Under Different FormationProtocols

Coin cell batteries 1 a and 1 b formed from composition 1 of example 1and a graphitic carbon counter electrode were activated under formationprotocols 1 and 2 of table 2 above, respectively, i.e. battery 1 a wasactivated at 4.6V and battery 1 b was activated at 4.35V. The batterieswere cycled at a rate of C/10 for the 1^(st) and 2^(nd) cycles, at arate of C/5 for the 3^(rd) and 4^(th) cycles, at a rate of C/3 for the5^(th) and 6^(th) cycles, at 1 C for cycles 7^(th) and 8^(th), at 2 Cfor cycles 9^(th) and 10^(th), and at C/5 for cycles 11^(th) and12^(th), respectively between 4.35-2.5V and the results are plotted inFIG. 2. As shown in FIG. 2, battery 1 a activated under formationprotocol 1 had higher specific capacity than battery 1 b activated underformation protocol 2, except for at rate 2 C. Thus, surprisingly, thebattery with only partial activation actually exhibited a greaterspecific capacity than the battery with full activation at a high rate.This result seems to imply that the retention of some lithium atcharging of the batteries under partial activation and correspondingmaximum potentials provides stabilization structure that provides morefacile lithium extraction at a higher rate.

Example 3 Evaluation of Batteries Based on Differential Capacity Plots

Coin cell batteries 1 c, 1 d, 1 e, and 1 f formed from composition 1 ofexample 1 and graphitic carbon counter electrode were activated at4.25V, 4.30V, 4.35V, and 4.5V respectively and tested for differentialcapacity. The results of differential capacity versus voltage areplotted in FIG. 3. As shown in FIG. 3, especially the enlarged portions3A and 3B, manganese activity is suppressed when the batteries arecycled up to 4.35V (1 e). However, when higher voltage such as 4.5V (1f) are used, there is an increase in Mn activity.

Coin cell batteries 1 g, 1 h, and 1 j formed from composition 1 ofexample 1 and lithium foil counter electrode were activated usingdifferent formation protocol and procedures and tested for differentialcapacity. The results of differential capacity versus voltage areplotted in FIG. 4. Specifically, for battery 1 g, the battery wascharged to 4.4 V in the first cycle and discharged to 2.0 volts. In thesecond cycle, the batteries were charged again to 4.4 V. The secondcycle did not show any activation. In the third cycle, the battery wascharged to 4.45 V and discharged to 2.0 V where some activation wasobserved. For battery 1 h, the battery was charged to 4.45 V in thefirst cycle and discharged to 2.0 volts. In the second cycle, thebatteries were charged again to 4.45 V. The second cycle did not showany activation. In the third cycle, the battery was charged to 4.5 V anddischarged to 2.0 V where some activation was observed. For battery 1 j,the battery was charged to 4.6 V in the first cycle and discharged to2.0 volts. In the second cycle, the batteries were charged again to 4.6V. The second cycle did not show any activation. In the third cycle, thebattery was charged to 5 V and discharged to 2.0 V where some moreactivation was observed.

As shown in FIG. 4, especially the enlarged portion 4A, when the highervoltages are reached in one step rather than multiple steps, significantactivation of Li₂MnO₃ is observed, which is indicated in FIG. 4A asshaded regions. The increased activation is noted graphically in FIG. 4Afor batteries 1 g and 1 h roughly by the two marked out areas.

Example 4 Evaluation of Batteries Based on Transition Metal Dissolution

The dissolution of Mn and other transition metals following formationwith either of formation protocols 1 or 2 was evaluated. Specifically,single layer pouch cell batteries with a single anode and a singlecathode with a separator in between were constructed usingcomposition 1. The batteries were charged to 4.3V, 4.35V or 4.6V at arate of C/10 using a two step charge protocol, with a constant currentcharge to 4.2V and after a 0 time rest period with a second charge atconstant voltage to the selected charge voltage. After formation, thebattery is stored at 100% state of charge (SOC) for 1 week. Thebatteries were then discharged to 0% SOC based on the voltage windowsoutlined in Table 3. The fully discharged batteries were thendisassembled and the anodes were removed and subjected to ICP analysesfor transition metal concentrations and the results are listed in Table3. The dissolution results demonstrated significantly more dissolutionof Mn at higher or wider formation window.

TABLE 3 Voltage window Ni Co Mn Formation Protocol 4.5 to 2.0 29 32 1901 4.35 to 2.0 57 51 185 1 4.35 to 2.5 15 8 68 2 4.35 to 2.0 17 11 91 24.3 to 2.5 13 9 71 2 4.3 to 2.0 13 11 80 2

Example 5 Resistances of Batteries Formed with Different FormationProtocols

Single layer pouch cells 1 k, 1 l, and 1 m formed from composition 1 ofexample 1 and graphitic carbon counter electrode were activatedfollowing formation protocols 1, 2, and 3 at 4.6V, 4.35V, and 4.3Vrespectively and tested for DC resistance (DCR).

To perform further pulse testing, the battery is charged and thensubjected to 1 C Pulse Test at room temperature (23° C.) with 10 secondpulses. In the pulse test, the DC resistance was evaluated as a functionof the state of charge starting from an initial 90% state of charge. Theresults of DC resistance in the pulse testing versus percentage of stateof charge (SOC %) are plotted in FIG. 5, in which 100% state of chargewas set at 4.35V for batteries formed with protocols 1 or 2 and at 4.3Vfor batteries formed with protocol 3. As shown in FIG. 5, all threebatteries have DCRs below 4 ohm between 20% to 90% SOC, and battery 1 kthat went through full activation had elevated DC resistance relative tothe batteries 1 l and 1 m that were subjected to the partial activationformation protocols.

Example 6 Battery Power Evaluation Based on State of Charge

Pouch cell batteries 1 n and 1 o with about 27 Ah capacities were formedfrom composition 1 of example 1 and graphitic carbon counter electrodefollowing the procedures above. The pouch cell batteries 1 n and 1 owere activated at 4.35V or 4.6V respectively and then tested for Regenpower and Discharge power at different percentages of state of charge.The evaluation of the different power values is described above beforethe Examples. Specifically, the batteries were discharged to aparticular state of charge, for example from full charge 100% SOC to 90%SOC. The batteries were then allowed to rest for one hour with nocurrent or voltage to equilibrate to its open circuit voltage (OCV). Thebatteries were then perturbed by a discharge pulse of 5 C magnitude for17 seconds followed by a charge pulse of 3.75 C magnitude for 10seconds. The drop in voltage during the discharge pulse and the rise inresistance in charge pulse of the batteries are recorded and used toevaluate the discharge power and Regen power of the batteries. Theresults of power versus percentage of state of charge (SOC %) areplotted in FIG. 6. As shown in FIG. 6, partially activated battery 1 nshowed higher power at lower stage of charge as the resistance is lower.For discharge power, lower stage of charge is particularly examined todetermine the operating SOC for the battery. The discharge power issomewhat greater at lower SOC for the partially activated battery incomparison with the fully activated battery. Regen power, however, isusually considered at higher SOC with respect to battery performance. Asshown in FIG. 6, the regen power is lower for the partially activatedbattery in, but the power achieved meets most electric vehicle andplug-in hybrid electric vehicle commercial targets.

Example 7 Evaluation of Batteries Formed with Different FormationProtocols

Two pouch cell batteries 1 p and 1 q designed to have roughly 1 Ah totalcapacity formed from composition 2 of example 1 and graphitic carboncounter electrode were activated following formation protocols 1 and 2at 4.6V and 4.35V respectively and cycled from 4.24V to 2.73V for 2500cycles at a charge rate of 1 C and a discharge rate of 2 C. The resultsof normalized discharge capacity and average voltage versus cyclenumbers are plotted in FIG. 7. As shown in FIG. 7, battery 1 p activatedwith formation protocol 1 has significantly decreased capacity andaverage voltage over large number of cycles. The batteries formed withthe partial activation protocol exhibited extremely stable capacity andaverage voltage for 2500 cycles.

Example 8 Calendar Life of Batteries at Different Temperatures

Two pouch cell batteries 1 r and 1 s designed to have roughly 1 Ah totalcapacity formed from composition 2 of example 1 and graphitic carboncounter electrode as well as a control battery were formed following theprocedure outlined above. The control battery was a cylindrical batteryessentially as described in Example 4 of published U.S. patentapplication 2011/0017528 to Kumar et al., entitled “Lithium IonBatteries With Long Cycling Performance,” incorporated herein byreference. Battery 1 r was activated following formation protocol 1 at4.35V while battery is was activated following formation protocol 3 at4.3V. The batteries were then stored at 4.35V (battery 1 r), 4.24V(battery is) and 4.2V (Control battery) at 30° C. for 12 months. Thebatteries were cycled once every month to determine the batterycapacity, and then returned to an 80% state of charge for continuedstorage. The permanent capacity loss of the batteries was tested duringthe 12 month periods, and the results are plotted in FIG. 8. Battery 1 rshowed the fastest permanent capacity loss. Battery is exhibited asignificant permanent capacity loss over the first month, but a veryslow decay after the first month that then extrapolates into a longcalendar life. The calendar life for battery 1 s is expected to be about14 years at 30 degree C. based on a linear extrapolation excluding the 0month data point. The calendar life for the control battery is expectedto be about 4 years at 30 degree C. based on a similar linearextrapolation.

Two additional pouch cell batteries 1 t and 1 u designed to have roughly1 Ah total capacity were formed from composition 2 of example 1 andgraphitic carbon counter electrode as well as a control battery wereformed following the procedure outlined above. The control batterycomprised a cylindrical battery as described above. Battery 1 t wasactivated following formation protocol 1 at 4.6V while battery 1 u wasactivated with formation protocol 3 at 4.3V. The batteries were thenstored at 4.3V (battery 1 t), 4.24V (battery 1 u) and 4.2V (controlbattery) at 45° C. for 12 months. Battery 1 t leaked after 4 months ofstore, and the failure of this battery is suggestive of poor storage forfully activated batteries out to 4.6V, possibly due to significantoxygen release during formation. The permanent capacity loss of thebatteries was tested during the 12 month periods and the results wereplotted in FIG. 9. The calendar life for battery 1 u is expected to beabout 2.2 years at 45 degree C. based on an extrapolation of the storageperformance over the last few months of the year. Battery 1 uexperienced significant permanent capacity loss over the first 7 monthsat 45 degrees, but then the performance decay flattened significantlyfor later storage times so that a 20% capacity loss was not experiencedbased on extrapolation until a reasonable period of time. The calendarlife for the control battery is expected to be about 1.2 years at 45degree C. All calendar life estimates were based on the last 5 months(8-12) of the 12 month data.

Example 9 Cycling Performance of Activated Batteries at DifferentTemperatures

Batteries were activated with different formation protocols to evaluatethe cycling performance of the batteries under acceleratedcharge/discharge conditions and at normal and elevated temperatures.

Pouch cell batteries 1 v and 1 w formed from composition 1 of example 1and graphitic carbon counter electrode were formed following theprocedures outlined above. Batteries 1 v and 1 w were activatedfollowing formation protocols 1 and 2, respectively. The batteries werethen cycled at 1 C for charge and 2 C for discharge between 4.35V and2.5V respectively at room temperature and the cycling results wereplotted in FIG. 10. As shown in FIG. 10, battery 1 v activated withformation protocol 1 is shown to lose specific capacity much faster thanbattery 1 w that was activated with formation protocol 2.

Pouch cell batteries 1 x and 1 y formed from composition 1 of example 1and graphitic carbon counter electrode were formed following theprocedures outlined above. Batteries 1 x and 1 y were activatedfollowing formation protocols 1 and 2, respectively. The batteries werethen cycled at 1 C for charge and 2 C for discharge between 4.35V and2.5V respectively at 45° C. and the cycling results were plotted in FIG.11. As shown in FIG. 11, battery 1 x activated with formation protocol 1is shown to lose specific capacity much faster than battery 1 y that wasactivated with formation protocol 2.

Example 10 Evaluation of Rest Period of Batteries Activated withFormation Protocol 2

Batteries activated with formation protocol 2 were evaluated withrespect to performance based on the length of the rest period. The restperiod is the storage period after initially charging the batteries to4.2V and before charging the batteries to 4.35V.

Pouch cell batteries a, b, c, d, and e designed to have roughly 1 Ahtotal capacity comprising composition 2 of example 1 and graphiticcarbon counter electrode were formed following the procedures outlinedabove. Batteries a-e were initially charged to 4.2V followed by a opencircuit rest period of 0, 2, 4, 6, and 10 days respectively before beingcharged to 4.35V. The batteries were then cycled for up to 300 cycles at1 C charge and 2 C discharge from 4.35V to 2V and the cycling resultswere plotted in FIG. 12. As shown in FIG. 12, batteries b-d appeared toexhibit comparable cycling performance. Battery a had slightly worsecycling performance and battery e showed significantly lower specificcapacity with cycling.

Example 11 Effect of Electrolyte Additive in Batteries Activated withFormation Protocol 2

The electrical performance of batteries with or without a lithium saltelectrolyte additive was evaluated during the course of formationprotocol 2.

Specifically, coin cell batteries f and g were constructed withgraphitic carbon active material, as described above for negativeelectrodes for batteries formed with lithium rich metal oxides, and alithium counter electrode with and without the lithium salt electrolyteadditive along with the electrolyte described above. The voltage versuscapacity performance of the batteries f and g were measured and recordedin FIG. 13. As shown in FIG. 13, battery f with additive appear to havea high initial voltage of about 1.6 V when the capacity of the batteryis essentially zero, indicating the additive reduction potential on theanode of the battery is about 1.6V. The battery without the additiveexhibited initial electrolyte reduction at a potential of about 0.9V.Reduction of the electrolyte with or without the lithium salt additiveis generally attributable to SEI layer formation.

A three electrode battery was assembled using a commercial test cell(HS-3E) configured for three electrode use with a cathode made fromcomposition 1 as the working electrode, graphite as the counterelectrode and lithium as the reference electrode in an electrolyte thatcomprises the lithium salt electrolyte additive. The voltages of thebattery during the two step formation protocol when cycled between thecathode and graphite or between the cathode and lithium were measuredand recorded in FIG. 14 as h and i, respectively. The portion of FIG. 14between zero and 2000 seconds was enlarged and shown as an insert. Asindicated in the insert, when cycled between the cathode and graphitethe additive was reduced at about 2.1V while when cycled between thecathode and lithium the additive was reduced at about 3.7V. Once the SEIlayer is formed, the difference between the battery potential and thepositive electrode potential becomes due to the graphite potential,which is relatively low against lithium. Thus, the difference betweenthe battery potential and positive electrode potential can be used toevaluate when the SEI layer is essentially formed in association withthe anode active material, which seems to be completed at some pointduring the first charge step.

The embodiments above are intended to be illustrative and not limiting.Additional embodiments are within the claims. In addition, although thepresent invention has been described with reference to particularembodiments, those skilled in the art will recognize that changes can bemade in form and detail without departing from the spirit and scope ofthe invention. Any incorporation by reference of documents above islimited such that no subject matter is incorporated that is contrary tothe explicit disclosure herein.

1. A method for the formation of a lithium ion secondary batterycomprising a lithium rich metal oxide composition, a negative electrode,a separator between the positive electrode and negative electrode, andan electrolyte comprising lithium ions, the method comprising:performing a first charge of the battery to a voltage from about 2.1V toabout 4.225V; after completing the first charge, holding the battery atan open circuit for a rest period of at least about 6 hours; andperforming a second charge after the completion of the rest period to avoltage from about 4.275V to about 4.39V.
 2. The method of claim 1wherein the first charge of the battery is to a voltage from about 4.15Vto about 4.22V.
 3. The method of claim 1 wherein the battery is held atan open circuit rest period from about 8 hours to about 8 days.
 4. Themethod of claim 1 wherein the second charge after the rest period is toa voltage from about 4.28V to about 4.38V.
 5. The method of claim 1wherein the lithium rich metal oxide is approximately represented by xLi₂MnO₃.(1−x) LiNi_(u)Mn_(v)Co_(w)A_(y)O₂, wherein z=0 and thestoichiometry defines x, u, v, w and y in terms of b, α, β, γ and δ, andwherein 0.125≦x≦0.325.
 6. The method of claim 1 wherein the negativeelectrode comprises graphitic carbon.
 7. The method of claim 1 whereinafter charging the battery to 4.35V and storing the battery at an opencircuit voltage for one week, the negative electrode of the batterycomprises no more than about 125 ppm of the combination of Mn, Co andNi.
 8. The method of claim 1 wherein after cycling for 2500 cyclesbetween 4.24V to 2.73V at a 1 C Charge and 2 C discharge, the batterymaintains at least 92% of capacity.
 9. The method of claim 1 wherein theelectrolyte comprises LiPF₆ and/or LiBF₄ at a total concentration fromabout 0.9M to about 2.5M and a solvent comprising ethylene carbonate andan organic solvent comprising dimethyl carbonate, methyl ethylcarbonate, γ-butyrolactone, γ-valerolactone or a combination thereof.10. The method of claim 9 wherein the electrolyte further comprises alithium salt additive.
 11. A lithium ion battery comprising a positiveelectrode comprising an active material, a negative electrode, aseparator between the positive electrode and negative electrode, and anelectrolyte comprising lithium ions, wherein the positive electrodeactive material comprises a lithium rich metal oxide that can beapproximately represented by the formulaLi_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2−z)F_(z), where b ranges from about0.01 to about 0.3, α ranges from 0 to about 0.4, β range from about 0.2to about 0.65, γ ranges from about 0 to about 0.46, δ ranges from about0.001 to about 0.15, and z ranges from 0 to about 0.2 with the provisothat both α and γ are not zero, and where A is a metal different fromNi, Mn and Co or a combination thereof, and wherein after charging thebattery to 4.35V at a rate of C/10, storing the charged battery with anopen circuit for a week at room temperature and fully discharging thebattery, the negative electrode comprises no more than about 150 ppm byweight manganese.
 12. The lithium ion battery of claim 11 wherein aftercharging to 4.35V and storing the battery in an open circuit voltage for1 week, the negative electrode comprises no more than about 135 ppm byweight manganese.
 13. The lithium ion battery of claim 11 wherein aftercharging to 4.35V and storing the battery at an open circuit voltage fora week, the negative electrode comprises no more than about 200 ppm ofthe combination of Mn, Co and Ni.
 14. A lithium ion battery comprising:a positive electrode comprising a positive electrode active materialthat comprises a lithium rich metal oxide; a negative electrodecomprising a lithium intercalation/alloying composition; a non-aqueouselectrolyte comprising lithium ions; a separator between the negativeelectrode and the positive electrode; and wherein the battery has beencycled through a formation cycle and wherein at the 200th cycle, thebattery has a specific discharge capacity based on the mass of thepositive electrode active composition of at least about 140 mAh/g at adischarge rate of 1 C from 4.35V to 2.0V that is at least about 97% ofthe 5th cycle specific discharge capacity.
 15. The lithium ion batteryof claim 14 wherein the lithium rich metal oxide is approximatelyrepresented by x Li₂MnO₃.(1−x) LiNi_(u)Mn_(v)Co_(w)A_(y)O₂, wherein z=0and the stoichiometry defines x, u, v, w and y in terms of b, α, β, γand δ.
 16. The lithium ion battery of claim 15 wherein 0.125≦x≦0.325.17. The lithium ion battery of claim 14 wherein the negative electrodecomprises graphitic carbon.
 18. The lithium ion battery of claim 14wherein the electrolyte comprises LiPF₆ and/or LiBF₄ at a totalconcentration from about 0.9M to about 2.5M and a solvent comprisingethylene carbonate and an organic solvent comprising dimethyl carbonate,methyl ethyl carbonate, γ-butyrolactone, γ-valerolactone or acombination thereof.
 19. The lithium ion battery of claim 14 wherein thepositive electrode active material has a discharge specific capacity ata rate of 2 C from 4.35V to 2.5V at the 10th discharge cycle that is atleast about 140 mAh/g and that is at least 87.5% of the dischargespecific capacity at a rate of C/5 from 4.35V to 2.5V at the 11thdischarge cycle.
 20. The lithium ion battery of claim 14 wherein thepositive electrode active material has a discharge specific capacity ata rate of C/3 from 4.35V to 2.5V at the 5th discharge cycle that is atleast about 160 mAh/g and having a calendar life at 85% state of chargeat 30 degrees C. of at least about 2 years based on discharge capacitydecay of no more than about 20%.
 21. The lithium ion battery of claim 14wherein the positive electrode active material has a stabilizationcoating over the lithium rich metal oxide.
 22. The lithium ion batteryof claim 14 having a discharge energy density of at least about 150Wh/kg at a discharge rate of C/3 from 4.35V to 2V.
 23. A lithium ionbattery comprising a positive electrode comprising an active material, anegative electrode, a separator between the positive electrode andnegative electrode, and an electrolyte comprising lithium ions, whereinthe positive electrode active material comprises a lithium rich metaloxide that can be approximately represented by the formulaLi_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2−z)F_(z), where b ranges from about0.01 to about 0.3, α ranges from 0 to about 0.4, β range from about 0.2to about 0.65, γ ranges from about 0 to about 0.46, δ ranges from about0.001 to about 0.15, and z ranges from 0 to about 0.2 with the provisothat both α and γ are not zero, and where A is a metal different fromNi, Mn and Co or a combination thereof, and wherein the positiveelectrode active material has a discharge specific capacity at a rate of2 C from 4.35V to 2.5V at the 10th discharge cycle that is at leastabout 140 mAh/g and that is at least 87.5% of the discharge specificcapacity at a rate of C/5 from 4.35V to 2.5V at the 11th dischargecycle.
 24. The lithium ion battery of claim 23 wherein the positiveelectrode active material has a discharge specific capacity at a rate of2 C from 4.35V to 2.5V at the 10th discharge cycle that is at least 89%to about 92.5% of the discharge specific capacity at a rate of C/5 from4.35V to 2.5V at the 11th discharge cycle.
 25. The lithium ion batteryof claim 23 wherein the lithium rich metal oxide is approximatelyrepresented by x Li₂MnO₃.(1−x) LiNi_(u)Mn_(v)Co_(w)A_(y)O₂, wherein z=0and the stoichiometry defines x, u, v, w and y in terms of b, α, β, γand δ, and wherein 0.125≦x≦0.325.
 26. The lithium ion battery of claim23 wherein the negative electrode comprises graphitic carbon.
 27. Alithium ion battery comprising a positive electrode comprising apositive electrode active material that comprises a lithium rich metaloxide, a negative electrode, a separator between the positive electrodeand negative electrode, and an electrolyte comprising lithium ions,wherein the lithium rich metal oxide can be approximately represented bythe formula Li_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2−z)F_(z), where b rangesfrom about 0.01 to about 0.3, α ranges from 0 to about 0.4, β range fromabout 0.2 to about 0.65, γ ranges from about 0 to about 0.46, δ rangesfrom about 0.001 to about 0.15, and z ranges from 0 to about 0.2 withthe proviso that both α and γ are not zero, and where A is a metaldifferent from Ni, Mn and Co or a combination thereof, and wherein thepositive electrode active material has a discharge specific capacity ata rate of C/3 from 4.35V to 2.5V at the 5th discharge cycle that is atleast about 160 mAh/g and having a calendar life at an 85% state ofcharge at 30 degrees C. of at least about 2 years based on dischargecapacity decay of no more than about 20%.
 28. The lithium ion battery ofclaim 27 wherein the positive electrode material has a calendar life at30 degree C. of at least about 3 years based on discharge capacity decayof no more than about 20%.
 29. The lithium ion battery of claim 27wherein the lithium rich metal oxide is approximately represented by xLi₂MnO₃.(1−x) LiNi_(u)Mn_(y)Co_(w)A_(y)O₂, wherein z=0 and thestoichiometry defines x, u, v, w and y in terms of b, α, β, γ and δ, andwherein 0.125≦x≦0.325.
 30. The lithium ion battery of claim 27 whereinthe negative electrode comprises graphitic carbon.